perfectly uniform from top to bottom of a column 20 cm. high, and it was concluded that the material which caused the coloration was not affected by gravitation. It was therefore suggested that the effect was due to matter in the colloid state (N.Z. Journ. of Sci. and Tech., 1928, vol. 9, p. 336).

At that time all the solutions available had been so diluted by the measures taken to determine the fineness of grain of the suspended matter that it was not practicable to investigate the supposed colloid material.

Further experiments have now been made and stronger solutions have been obtained. In a particular instance, 5,000 grams of greywacke gravel of the following grades were used: 7.62 - 6.35 cm., 762.5 gm., 6.35 - 5.71 cm., 1694.2 gms., 5.71 - 5.08 cm., 1698.7 gm., 5.08 - 3.81 cm., 799.6 gms., 3.81 - 2.54 cm., 44 gm.

After movement for 24 hours in 2 litres of water at the rate of 32 turns per minute, approximately 1 mile per hour, 307 grams of suspended matter finer than 0.07 mm. in diameter were produced. A dark reddish-yellow but transparent liquid, uniform in appearance throughout, remained after 100 days' settlement.

The liquid was strongly opalescent. When 100 cc. were evaporated, 0.147 grams of material remained on the dish. Of this 0.048 grams were dissolved on treatment with water and were afterwards found to be sodium carbonate. The total amount contained in solution in 3850 cc. of water was therefore 5.66 grams of which 1.31 grams were sodium carbonate, leaving in the water 4.35 grams of suspensoid material which did not settle.

Much of this material was deposited when half of the liquid had been evaporated. Before the residue became dry a gelatinous condition was noticed.

This residue was fused with sodium carbonate and its constituents were estimated by the ordinary methods of silicate analysis, when the substances isolated gave the following percentages. Table 1, No. 1.

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In all probability 90 per cent. or more of the iron was derived from the iron container. If the amount derived from the rock is estimated as 3 per cent., there is left 18.80 per cent. as the amount derived from the container. If this were in the form of ferric hydrate it would have 3 per cent. of water combined with it. The material presumably derived from the rock is thus reduced by 21.80 per cent. If the composition is recalculated on the new basis the result in Table 1, No. 3 is obtained.

This result agrees rather closely, as far at least as the main constituents are concerned, with an analysis of abyssal red clay quoted by Clarke (Data of Geochemistry, 1911, p. 489) as typical of that material Table 1, No. 4. On the other hand, Clarke (l.c., p. 490) gives a composite analysis of 51 samples of red clay (Table 1, No. 5) by Hillebrand and Sullivan. Here it is noticeable that alkalies which do not appear in Brazier's analysis amount to 4.90 per cent.; with potash in excess of soda.

The tendency of the alkalies to combine with some of the metallic oxides under deep water abyssal marine conditions is, however, demonstrated by the occurrence of phillipsite crystals so frequently in red clay and of glauconite in off-shore sediments. In both of these substances potash is in greater amount than soda.

The similarity of the composition of this colloidal matter to that of red clay is possibly of no importance, as the two main constituents at least have much the same proportions as they have in the average composition of the surface rocks of the earth (Clarke l.c., p. 32). It is, however, suggested that there may be some significance in the resemblance as showing that a possible origin of the red clay may be found in colloid matter, formed by abrasion on coast-lines, which in the state of minute floccoids might well be distributed over the uttermost parts of the ocean.

It is notable that potash is in greater amount than soda in the analyses of shale as quoted by Clarke (l.c., p. 32), the relative amounts being 3.24 per cent. potash and 1.30 per cent. soda. These substances must ultimately have been derived from igneous rocks in which the average relative percentages are potash 2.99 and soda 3.40.

It would seem from this that either the potash silicates are less affected by processes of destruction than the corresponding sodium silicates or that the potash of the soluble sea salts enters into combination with silica more readily than soda. This may be related to the ascertained fact that soil retains the potassium of a solution of salts of that metal (Clarke, l.c., p. 211).

The general occurrence of phillipsite and frequent presence of glauconite, in regions to which colloid matter only could be borne— unless the idea of decomposition of floating pumice be accepted—supports the suggestion that potash contained in the dissolved salts of sea-water can enter into combination with silica and hydroxide of iron and alumina when in the colloid state.

A distinctly different view is put forward by Clarke (l.c., p. 128): “The oozes of the deep sea have been partly leached of their alkalies, but some of the potassium of the original volcanic material has been retained in the formation of zeolites. Nearer land potassium has been used in the formation of glauconite and still nearer when mechanical sediments appear a similar discrimination is evident— sodium is dissolved and potassium is held back.”

In discussing the formation of glauconite, Clarke says (Clarke, l.c., p. 578): “Probably in all their occurrences the final reaction is the same, namely, the adsorption of potassium and soluble silica by colloidal ferric hydroxide. In the ocean these materials are prepared by the action of decaying animal matter upon ferruginous clays and fragments of potassium bearing silicates.”

Scott makes the following suggestion: “At some stage during the deposition of sediment the latter may contain rock detritus in such a state of decomposition that it readily on hydration assumes a gel form. This gel will consist mainly of silica with subordinate alumina and ferric oxide. Percolating solutions containing alkalies, iron salts, etc., will be liable to diffuse through the gel moss and during this diffusion the salts will undergo differential adsorption. Ferric oxide will be precipitated while potash will be adsorbed in preference to soda. The well-known occurrence of greater amounts of the former in preference to the latter in clays and soils is in favour of this differential action. Finally the gel will harden to give glauconite.” (A. Scott, “The application of colloid chemistry to Mineralogy and Petrology,” B.A.A.S., 4th Rep. on colloid chemistry, 1921, p. 237).

Harrison and Jukes separated the pumiceous matter in a sample of oceanic red clay by chemical means and state that it was apparently unaltered. This suggests that silicates remain unaltered under deep water oceanic conditions. (Harrison and Jukes Brown, “Chemical Composition of Oceania Deposits,” Q.J.G.S. 51, 1895, p. 315).

The solution obtained from the container in which the abrasion had been performed was submitted to several tests, as follows:—(1) Ammonia gave no precipitate. This seemed significant seeing that a third of the matter in solution consisted of iron and alumina. (2) Hydrochloric acid even in small quantity at once gave a large precipitate. (3) Flocculation took place quickly when sea water was added. In different tests the substances were mixed in the following proportions:

In the last two cases the floccules separated and subsided very slowly. When the sea water was 250 times the volume of the colloid solution ten hours were required for settlement through 5 cm. The floccules broke up at once when the liquid was agitated and subsequently took rather longer to form than in the first instance. (4) When the terminals from a small six-volt electric battery were placed in the