(1.) Peridotites and Serpentines.
The rocks collected in situ from the flanks of the Olivine Range are mainly wehrlites and dunites with less common lherzolites, nearly always partially serpentinised, usually fine - grained, and dark greenish grey in colour. Those specimens in which serpentinisation is far advanced break with the fine flaky or somewhat splintery fracture characteristic of antigorite rocks.
Though a large number of sections were examined, no trace of regular gradation in mineralogical composition or in degree of serpentinisation across the intrusive mass could be observed. Red Spur and Martyr Spur consist mainly of wehrlite, with some dunite, both of which may occasionally contain small amounts of enstatite, while dunite is developed in abundance on the southern flank of Martyr Spur where it falls away into the precipitous gorge of Woodhen Creek. Numerous dykes of pyroxenite and other rocks of a hypabyssal nature invade the main formation throughout, but these will be considered separately under (2).
Evidence of shattering is always prominent and in some places, e.g. in the gorge of Woodhen Creek, below Mt. Richards, there are zones of intense crushing and slickensiding. Chrysotile veinlets, usually about 5 mm. but sometimes reaching 20 mm. in width, are very numerous along the fracture lines throughout the whole peridotite formation.
Boulders of chromite occur in a number of places on the slopes of Martyr Spur, but no masses of any great size were seen in situ.
Descriptions of typical rocks are given as follows:—Number 1225 (Red Spur). The rock is an altered wehrlite which consisted originally of olivine about 75%, and diallage 25%, with minor amounts of chromite. The olivine has been much shattered and about three-quarters or more of it has been converted to colourless antigorite (Figs. 10, 11) plates and blades of which project radially inward from the cracks into central cores of still fresh olivine. In parts of the section all the olivine has thus been replaced by parallel, tufted and sometimes interwoven crystals of antigorite, but the positions of the cracks in the original olivine are still marked by fine lines of extremely minute dark particles, probably of magnetite. This latter mineral, as usually is the case in rocks of this area, is never developed in any quantity, as a result of the change from olivine to antigorite. The pyroxene occurs in rather irregular crystals from 1 mm. to 2 mm. in diameter, which sometimes enclose poikilitically smaller masses of olivine. It is always altered to a semiopaque brownish product which appears white in reflected light, though the polarisation tints of the pyroxene still show through when it is viewed between crossed nicols. Complete extinction of any one crystal cannot be obtained, but the extinction angle measured upon those small fragments of the mass which are clearest and least altered as seen under high magnification, indicates that the original pyroxene was monoclinic. Alteration of aluminous pyroxene in this way is a constant feature in the rocks of this area. Small amounts of antigorite
may also be developed along the cleavage cracks of the altered pyroxene, while a considerable quantity of secondary magnetite is often produced, especially round the borders of the pyroxene crystals.
Number 1226 (Red Spur). Thus is a much altered lherzolitic rock which probably consisted originally of olivine 80%, augite 10% and enstatite 10%, with a small amount of accessory chromite. The olivine shows perfectly developed mesh structure the cracks being sharply defined by a semiopaque mixture of fine talc (?) and a very little magnetite dust. The intervening grains have been replaced almost completely by blades of antigorite between which the residual remnants of olivine, though small, are clearly visible under high magnification. The aluminous pyroxene is partly clear, but in most cases has been altered to the usual almost opaque white replacing product. Orthorhombic pyroxene was not definitely determined, but there are a number of patches of coarse strongly birefringent talc with numerous grains of secondary magnetite throughout, and in view of the distinctive types of alteration constantly shown by the augite and the olivine respectively, it is thought probable that the talc-magnetite aggregates represent an iron-bearing enstatite in the original rock.
Number 1227 (Martyr Spur, half-mile below the bush line). The rock is a serpentinised dunite showing perfect mesh structure. The meshes consist of normal chrysotile serpentine spotted with strings of magnetite grains, but the enclosed cores of olivine have been converted largely to flakes of antigorite between which tiny remnants of olivine still persist.
Number 1228 (Martyr Spur, quarter-mile below the bush line). This is a partially serpentinised wehrlite very similar to Number 1225 from Red Spur.
Number 1229 (Martyr Spur, just below the bush line). Nearly 70% of the rock consists of a fine lattice of clear antigorite crystals which seem to have been derived largely from pyroxene, though probably to a minor extent also from olivine, small residuals of which occur throughout. The former mineral is mostly augite, but includes also a small proportion of enstatite, and occurs in crystals which may reach 1 mm. in length. Some of this augite has been altered to the usual brown dusty aggregate, but mostly it is in fairly clear ragged remnants and small cleavage fragments obviously in the process of being converted directly into antigorite. Secondary magnetite is fairly abundant.
Number 1230 (Martyr Spur at the bush line). In hand specimen this is a homogeneous, fine-grained, dark green serpentine with well marked flaky fracture. The section is clear and transparent and consists almost entirely of antigorite, with a little secondary magnetite and a small percentage of dusty brown opaque material representing aluminous pyroxene. In a number of places in the section there are remnants of what have been crystals of bastite showing a striking transition to antigorite into which they are now more than half converted.
Number 1231 (Martyr Spur, one quarter-mile above the bush line). This is a serpentinised dunite consisting almost entirely of altered olivine with about 5% brown opaque altered augite.
Number 1232 (Crest of Martyr Spur half-a-mile above the bush line). This is a fine-grained grey rock which in section proves to be a-half serpentinised wehrlite consisting originally of 70% olivine, 25% augite, two or three small crystals of enstatite and accessory chromite. As usual the olivine is shattered and shows perfectly the transition to antigorite, blades of which not only project radially inwards from the cracks, but also stab in every direction through all parts of the olivine grains. The crystals of monoclinic pyroxene show the usual alteration to brownish almost opaque aggregates white in reflected light, with fringing rims of dusty magnetite, but the enstatite on the other hand is unaltered except for the presence of a narrow border of fine magnetite.
Number 1233 (Martyr Hill, twenty-five yards from the eastern boundary of the peridotite mass). The rock is a wehrlite similar to the section previously described except that it is less altered. Antigorite needles are only just starting to form through the olivine, while the pyroxene, though partially altered in the usual way, is still sufficiently clear to show the extinction angle. So that it may definitely be determined as monoclinic. Strings of secondary magnetite occur along the cracks on the pyroxene and to a less extent in the olivine also. Enstatite is absent, but chromite is present in accessory amount.
Numbers 1234 and 1235 (Upper part of creek draining the southern side of Martyr Hill). The rock is a banded dunite consisting entirely of olivine and chromite, the latter being present in amounts ranging from 15% to 30% of the whole rock. In hand specimen the olivine appears fresh and clear, but high magnification beneath the microscope reveals incipient alteration to antigorite, while two or three veinlets of chrysotile occupy major cracks. The rock merges into a perfectly fresh clear dunite carrying about 2% chromite, which continues in abundance down the creek to the bottom of the gorge of Woodhen Creek. In this rock (Number 1236) needles of antigorite are very rare, though the olivine is much crushed.
The specimens collected by Mr. Moir from the vicinity of the Red Mountain include several representing the normal peridotite as well as a number of interesting dyke rocks which invade the main intrusion and will be described in the next section.
Number 1237 (western margin of Red Mountain intrusion, east of Awarua Bay). This is a greenish partially serpentinised wehrlite consisting originally of olivine (about 80%) and augite (about 20%) with some accessory magnetite. The main constituent is antigorite, through which are scattered small remnants and cleavage prisms of olivine with feathery margins where they pass into antigorite. The olivine grains show undulose extinction but lack the shattering which is such a constant feature of the rocks previously described. The pyroxene is altered to the usual brownish decomposition product. Number 1238 (Red Mountain) is a yellowish dunite which in section appears quite fresh. There is a small amount
of chromite, and in the hand specimen a single crystal of bright green chrome-diopside was observed, similar to that which is developed in some of the dykes of pyroxenite and was described by Ulrich (1890) from this area.
The Pleistocene drift which covers the whole of the Cascade Plateau consists very largely of huge boulders of peridotite which probably include material brought from along the full length of the Cascade Valley. The prevailing rock type (e.g. Numbers 1239, 1240 and 1241, from Laschelles Creek) is a fresh clear green dunite in which darker grains of pyroxene are present to the extent of about 5% or 10% so that the rock may approach to harzburgite in composition. The olivine is much crushed and has undulose extinction, but it is either quite fresh or exhibits merely the incipient stages of alteration to antigorite. The pyroxene is enstatite, usually almost clear and transparent, and sometimes shows bent cleavage lamellae. A small amount of chromite also is present. Number 1242 (from drift beside the track one quarter mile above the ford across the Martyr) is a rather similar looking rock, which on sectioning is found to contain about 15% much altered augite and about 85% olivine which in places has been converted to antigorite. This may be classed as a wehrlite.
Number 1243 (Boulder from Martyr Ford) is a fine-grained green serpentine which consists mainly of fine antigorite together with a few crystals of basite about 1 mm. in length. There is abundant secondary magnetite and a few small patches of secondary carbonate.
Number 1244 (from drift between Jackson Saddle and Martyr Bridge) is a green semitranslucent serpentine which breaks with the characteristic splintery fracture of antigorite, and resembles nephrite but for its inferior hardness (about 5 to 5½). In thin section 90% of the rock is seen to consist of fine blades of antigorite (Fig. 12) about 0.1 mm. to 0.2 mm. long, showing most perfectly the “thorn structure” of Bonney. About 5% of the rock consists of a very pale green mineral with similar structure, sometimes distinctly pleochroic with absorption × < Z. The crystals are elongated parallel to Z. The refractive index is slightly higher than that of antigorite, but the birefringence is distinctly greater (about 0.02) giving interference tints as high as red of the first order when the antigorite gives only greys and whites. Convergent light tests show that the mineral is biaxial and positive, with a small optic axial angle. This latter character and the higher double refraction distinguish it definitely from antigorite. The mineral appears to lie between chrysotile and xylotilite, and may be identified as an iron-bearing chrysotile or iron-poor xylotilite. Bastite also occurs in rather small amounts (about 5%) and appears in ordinary light as patches having slightly lower refractive index than the surrounding mass of antigorite crystals. The mineral shows a negative biaxial interference figure. Under high power the bastite is seen to be in the process of being converted to antigorite, needles and blades of which are forming in all directions throughout every crystal of bastite. Similar replacement of bastite has been described and figured by Benson (1914, pp. 674, 675) from serpentines in New South Wales.
(2.) Dykes invading the Peridotites.
Dykes and veins of pyroxenite, usually only a few inches in thickness, occur abundantly invading the peridotite mass along the whole of its extent. Similar rocks are represented among the specimens collected by Mr. Moir from Red Mountain district, and were found also as small dykes and veins traversing the dunite and wehrlite of large boulders, among the drift material of the Cascade Plateau. The abundance of these dykes probably accounts for the statement made by Ulrich (1890) who in describing the Red Mountain mass notes that “the olivine and enstatite vary much in relative proportions; while in some specimens the former greatly predominates over the latter, in others the reverse is the case.” Professor Ulrich was working on specimens collected by prospectors and others; but recently obtained field evidence shows clearly that peridotites with a high olivine content constitute the main intrusive mass and that pyroxenites are minor features only.
The pyroxenites of the Olivine Range consist essentially of augite and enstatite in varying proportions, the former usually dominant, and occasionally there may be a little olivine. Many of these rocks show the effects of intense alteration which has followed along lines entirely different from those shown by the peridotites, in which conversion of olivine to antigorite, augite to a brown opaque decomposition product, and enstatite to bastite or antigorite are such constant features. Typical pyroxenites in various stages of alteration are described below:—
Number 1245 (Martyr Spur half a mile above the bush line). Dillage in subidiomorphic crystals about 2 mm. long, occasionally showing Schiller structure and always unaltered except for a slight dusting of brownish material, makes up 80% of the rock, while there are also one or two clear crystals of enstatite. The remainder consists of clear interstitial patches of antigorite, which enwrap the pyroxene and probably represent original olivine, small grains of which still remain in the surrounding mass of antigorite laths.
In Number 1246 (boulder, Cascade Plateau) over 95% of the rock is pyroxene, enstatite greatly predominating over augite, while a very little olivine and a few grains of chromite also are present. All the minerals are quite fresh. Number 1247 (Red Mountain) is also an undecomposed enstatite-rich type, which contains also about 25% of augite and a small amount of chromediopside. The latter mineral is brilliant emerald green in hand specimen but pale green and transparent in section. As noted by Marshall (1906, pp. 564, 565), Ulrich (1890) did not examine this latter mineral in section but identified it provisionally as enstatite. Marshall, however, definitely determined as chrome-diopside a similar mineral from the lherzolite of Cow Saddle, some twenty-five miles south of Red Mountain, and suggested that the green pyroxene from this latter locality would prove to be the same mineral.
Number 1261 (Red Mountain mass, east of Awarua Bay) is a dark green slickensided serpentine which breaks with a flaky “antigorite” fracture. The rock appears originally to have been a pyroxenite but is now more than half converted to antigorite.
Augite and enstatite are both present, but the former mineral greatly predominates over the latter. Both pyroxenes originally occurred as large crystals reaching 3 mm. in length, which are now much broken down and in many parts of the section are represented only by aggregates of small clear cleavage prisms and grains. The transition of both pyroxenes to antigorite is perfectly shown (Figs. 19, 20). Magnetite is present in accessory amounts both as a primary mineral, and also as strings thrown out along the cleavage planes of the altered pyroxene.
Number 1248 (Martyr Spur, one-third of a mile above the bush line). In hand specimen this is a greyish serpentinous rock in which small crystals of pyroxene are visible. The greater part of the rock consists of small plates of pennine with characteristic greenish grey anomolous interference tints, interspersed with less plentiful blades of antigorite and numerous small remnants of clear monoclinic pyroxene. In some parts of the section small grains (0.05 mm.) of deep red garnet are scattered in small amount through the aggregates of pennine and antigorite, usually in the vicinity of grains of magnetite. Apparently the rock consisted in the first place largely of aluminous pyroxene, which has since been altered to pennine, and a little antigorite, garnet and magnetite, through which small cleavage prisms and grains of residual pyroxene still remain in small proportions. Between these aggregates are also present smaller patches of clear felted antigorite, probably pseudomorphous after enstatite or olivine, though no trace of either mineral remains.
Number 1249 (Martyr Spur, three-quarters of a mile above the bush line). In hand specimen this is a coarse-grained rock in which abundant grey serpentinised pyroxene together with large crystals of green chlorite, bright unweathered magnetite and one crystal of reddish-brown garnet were determined. Apparently both monoclinic and orthorhombic pyroxenes were present in abundance in the unaltered rock. The former is now represented by a very fine felt of antigorite in which cleavage prisms of the original mineral still persist in one or two places in the section. The enstatite has been replaced completely by a mixture of coarse talc and finer antigorite (Fig. 13). Sometimes almost the whole of the pseudomorph consists of talc, while in other cases alternating bands of talc and fine antigorite have formed parallel to the cleavage of the original enstatite. About 5% of the rock consists of antigorite pseudomorphous after olivine. Though this mineral is completely replaced, its former presence is indicated by the characteristic curved cracks which are now defined by strings of magnetite dust. There are several very large crystals of magnetite, but neither the garnet nor the chlorite seen in the hand specimen were observed in the section.
Number 1250 (Martyr Spur, a-quarter of a mile above the bush line). The main constituent is augite (60% of the rock) the crystals of which are considerably dusted with brown decomposition products but are still definitely determinable. Pennine in clear subdiomorphic crystals about 1 mm. in diameter showing the usual greyish-green interference tint, occurs between the crystals of augite from which it seems to have been derived. Red garnet in
granular masses up to 0.2 mm. long is usually to be found associated with the pennine, but may occur in the pyroxene as well. Secondary magnetite is also fairly plentiful. In other parts of the section large crystals of augite pass into a frayed mass of small prismatic crystals of colourless diopside associated with which are small amounts of garnet, pennine and magnetite. The transition from augite to diopside is sometimes perfectly shown under high magnification. There are also several crystals, ranging up to 2 mm. in length, of a striking pale golden yellow mineral which is probably an iron-rich or titaniferous variety of olivine. There is strong pleochroism with × = golden yellow and Z = almost colourless or very faint yellow. The extinction is straight parallel to a distinct prismatic cleavage, which is the Z direction of the crystal. In several cases crystals were found to consist of three or four twinned individuals. The refractive index is fairly high and the birefringence is about equal to that of the augite. Convergent light tests indicate that the mineral is biaxial with an optic angle near 90°, so that the sign could not be determined.
Number 1251 (Red Spur). Relatively clear monoclinic pyroxene in crystals one or two millimetres long makes up 30% or 40% of the rock and passes gradually into a finely crystalline mass of pennine with greyish-green interference tints, through which residual grains and small cleavage prisms of the original pyroxene are scattered plentifully in some parts of the slide. In other parts, fine pennine has been developed in well defined bands along the cleavage cracks of the pyroxene crystals. There are also present numerous sharply bounded areas about 1 mm. to 2 mm. in length, which consist largely of granular reddish brown material much of which shows up white in reflected light. Some of this substance appears under high magnification to be translucent and is probably much altered sphene partially coated with leucoxene. Included among the grains are small amounts of pennine and serpentine.
Number 1252 (Gorge of Woodhen Creek). The specimen was collected from the great mass of crushed and slickensided green serpentinous rock which outcrops at the junction of the creek draining the south side of Martyr Hill with Woodhen Creek. Veins of chrysotile are abundant in the hand specimen. The rock appears to have consisted originally almost entirely of monoclinic pyroxene which is still present in considerable quantity. Much of the mineral has been converted to antigorite which now occurs in rounded flakes which may reach 0.5 mm. in diameter and which clearly show a definitely negative optical sign. In some crystals this alteration has taken place along the cleavage cracks of the pyroxene. Throughout most of the section, however, an unusal type of mesh structure has been developed on a very perfect scale (Figs. 17, 18). The rounded plates of antigorite referred to above are separated from one another by a meshwork built up of grains and prismatic fragments of clear transparent monoclinic pyroxene which at first sight appears from its very mode of occurrence to be secondary in origin. Careful inspection, however, reveals that this interstitial pyroxene is similar to and apparently continuous with the
undoubtedly primary pyroxene, which in other portions of the slide shows normal alteration to antigorite along the cleavage planes as already noted. It is suggested therefore that the curious mesh effect has arisen by the alteration of pyroxene to antigorite, crystals of which, in growing outward from points within the pyroxene crystals, have gradually replaced the latter mineral to a large extent, leaving borders of shattered residual pyroxene separating adjacent plates and masses of antigorite from one another. A further complication has been introduced by subsequent shearing and shattering of the whole rock, after which microscopic veins of chrysotile have been formed along the cracks so produced. In some parts chrysotile appears to have replaced completely the previously formed antigorite so that there are large patches of normal chrysotile serpentine enclosing grains of residual pyroxene, which lie adjacent to the aggregates of antigorite and pyroxene just described. Pressure effects are seen in the universal undulose extinction of the antigorite and in pronounced bending of some of the veins of chrysotile.
Number 1253 (Boulder, Martyr Ford). The rock is a green serpentine which seems originally to have consisted almost entirely of clear transparent monoclinic pyroxene, half of which is now converted to chrysotile serpentine. The transition is perfectly shown. In some parts of the section there is a tendency for the serpentine to show rough antigorite structure, and it is possible that this mineral has been developed in small amount from the chrysotile as a result of pressure. A single large crystal of bastite was noted, while there are also several veinlets of talc running through the mesh of chrysotile. A small amount of secondary magnetite is present in some parts of the section.
Although recorded by Ulrich (1890) from the Red Mountain area, dykes of normal gabbro-pegmatite were not found at all in the district described in the present paper. Dykes of light-coloured rocks were occasionally met with, however, and microscopic examination shows that these vary considerably in composition.
Number 1254 (Martyr Spur). The specimen was obtained from a dyke of hard white rock several feet in width, which cuts the peridotite mass and outcrops on the crest of Martyr Spur just where the heavy bush gives way to subalpine scrub. The rock is much altered, and under low magnification appears to consist largely of semiopaque white material interspersed with clear irregular patches of finely felted antigorite which constitute 15% of the section. There are also one or two large crystals of unaltered diopside the margins of which feather out into the antigorite. Under high power, the white almost opaque mass is seen to consist largely of colourless grossularite in very small clear grains, intimately associated with which are slender prisms of secondary pyroxene and laths of antigorite. Most of this pyroxene is enstate, but diopside is also present. There is a small quantity of secondary magnetite and also what appear to be residual altered grains of original pyroxene in some parts of the section. The rock is clearly allied to the garnet-pyroxene rocks of the peridotite belt of Nelson, to which Marshall (1911) gave the name, rodingite. Benson (1918, p. 686)
noted very similar rocks in the Great Serpentine Belt of New South Wales. One of these he describes as consisting entirely of garnet containing lakelets of antigorite which represent original pyroxene, and he notes at the same time that the garnet has encroached considerably upon the pyroxene boundary. In a recent paper Grange (1927, pp. 162-163) mentions the frequent presence of diopside, zoisite and prehnite in the Nelson rocks, but apparently secondary enstatite, though so abundant in the rock just described, is absent both from the rodingites of Nelson and the similar garnetiferous rocks from New South Wales.
Number 1255. The specimen was obtained from a narrow dyke of hard even-grained white rock which cuts the peridotite mass about half-way down the gorge of the creek flowing from the southern slopes of Martyr Hill into Woodhen Creek. The rock consists almost entirely of albite and quartz in equal proportions. The albite occurs in tabular crystals about 3 mm. in length, and is much crushed and shattered into smaller angular fragments in many parts of the slide. Much of it is untwinned, though albite twins were seen in several instances, but the low refractive index and definitely positive optical character in every case allow the mineral to be determined with certainty. The large crystals of albite are set in a matrix (Fig. 14) which consists almost entirely of much crushed quartz in irregular grains ranging from 0.05 mm. to 0.5 mm., which show undulose extinction between crossed nicols. Epidote occurs in strings of small grains along the junctions between the large feldspars and the surrounding mass of quartz grains, and in several places is developed as veinlets along cracks. Benson (1918, p. 691) has described similar rocks from dykes cutting the peridotite of the Great Serpentine Belt of New South Wales. The writer has been fortunate enough to have had the opportunity of examining Professor Benson's sections, one of which (M.B. 230) is almost identical with the rock just described.
Number 1256 (Boulder, Martyr Ford). In hand specimen the rock is white with ill-defined bands of a light brownish tint. In section the most conspicuous mineral is tremolite, which occurs in clear prismatic crystals (0.5 mm. × 0.1 mm.) and ragged torn flakes of similar size, which are set in a very fine crushed matrix consisting of tremolite, antigorite and a small amount of a clear mineral with refractive index less than that of Canada Balsam—probably albite. The prisms of tremolite frequently show simple twinning. There are also a few small crystals of augite and several grains of magnetite in the process of being converted to limonite. The rock probably represents an extremely crushed and altered gabbroid dyke-rock originally very rich in pyroxene.
Number 1257 (Boulder, Martyr Ford). In hand specimen this is a whitish or light grey homogeneous fine-grained rock with a flaky fracture. Under low magnification, the section is seen to consist for the most part of a finely granular almost opaque white matrix through which are streaked irregularly drawn out patches of clear transparent material which make up about one-fifth of the rock. Under high power the white semiopaque matrix appears
to be made up almost entirely of granular pleochroic yellowishgreen epidote, intermixed with much less abundant, fine, transparent grains which are probably albite and quartz. One or two tiny crystals of brown hornblende and a little zoisite were also noted. The clear lenses and streaks consist mainly of albite or oligoclase-albite intermixed with smaller amounts of finely granular quartz. The albite is water-clear and sometimes shows polysynthetic twinning. In one or two cases crystals ranging up to 1 mm. in length were observed, but usually the mineral is in small interlocking grains. In hand specimen the rock closely resembles specimens of “white gabbro” or gabbro-granulite collected by Professor W. N. Benson from Carrick Luz in the Lizard district of Cornwall, and described by Flett and Hill (1912, pp. 87-90). In these, however, the pyroxene is granulated and often converted wholly or partially to amphibole while the feldspar either goes over to saussurite or is simply crushed; but in Number 1257 described above there has been interaction between the augite and plagioclase, which have ultimately been altered to epidote, albite and a little quartz—a reaction involving loss of magnesium.
Number 1258. The specimen was collected by Mr. Moir from a dyke in the peridotite near the summit of Red Mountain. About half the rock consists of large idiomorphic crystals of hornblende (about 1.5 mm. × 1 mm.), yellowish to brownish green in colour, which sometimes is simply twinned. These are set in a fine granular mass the main constitutent of which is zoisite showing strong Prussian blue interference tints, together with minor quantities of albite and quartz. Sometimes the interstitial albite is in crystalline continuity throughout patches as much as .25 mm. in diameter, the twinning lamellae also being continuous across this distance. There is a small amount of rather indefinite chlorite, while a single crystal of tremolite, bordered with brown hornblende, was observed. The rock probably represents a gabbroid dyke, in which the augite has been converted to hornblende and the labradorite to zoisite and albite. Recrystallisation must, however, have been very complete since the hornblende now shows no trace of secondary origin.
Number 1259 (Dyke, Red Mountain). This also is a much altered dyke rock consisting mainly of hornblende and altered feldspar in equal proportions. The hornblende is in large ragged prismatic crystals, often showing bent cleavage lamellae, and a curious pinkish brown in colour. The pleochroism is strong (absorption Z > Y > X), the extinction angle is 18°, the elongation is positive and the opticial sign negative. In parts of the section the hornblende passes into tufted groups of slender prisms of tremolite. The feldspar is intensely altered to an almost opaque white aggregate which appears to be largely zoisite and quartz. Secondary epidote and clear quartz occur in small veinlets occupying cracks.
Number 1260 (Vein in peridotite, Red Mountain). This is an interesting rock which in hand specimen is very hard, finely granular, irregularly streaked and pinkish in colour. It consists
almost entirely of clear unaltered monoclinic pyroxene (probably diopside) in crystals ranging up to 2 mm. and a slightly less amount of pale pink faintly pleochroic vesuvianite. The latter mineral may easily be distinguished by its colour, high refractive index, very low double refraction giving an anomolous greyish green interference tint, distinct prismatic cleavage parallel to which there is straight extinction, uniaxial negative interference figure and negative elongation parallel to the vertical axis. In some cases it has formed as borders round crystals of diopside, while in others it appears to be enclosed by that mineral. Veinlets of zoisite 0.2 mm. wide cut the section sharply in one place. In another section (Number 1260a) of the same rock, streaks consisting almost entirely of aggregated prisms and grains of diopside were noted, while about 1% of the rock consists of green pennine scattered in small patches throughout the main mass of pyroxene and vesuvianite. Grange (1927, p. 163) mentions the occurrence of vesuvianite in the fine-grained “rodingites” of Nelson, and calls attention to the presence of grossularite, diopside and vesuvianite in veins described by Graham (1917) from the serpentines of Quebec.