A peculiar feature of the Ostrea beds, perhaps most marked in Boby's Creek, is the strong smell of petroleum given out when the oyster-shells are freshly broken. I submitted specimens to the Dominion Analyst, but he reported that only a trace of petroleum could be determined analytically. The black colour of the oyster-shells and the odour of petroleum appear in New Zealand to be practically confined to the Piripauan Ostrea beds of North Canterbury. McKay's Creek.—McKay collected in 1874 from the Ostrea beds of McKay's Creek, which is presumably one of the creeks entering the Waipara River from the north, above the limestone gorge, but he gave no detailed account of the beds in this locality. Woods determined from his collections the following species: Nemodon sp. and Pecten (Camptonectes) hectori Woods. Birch Hollow (Plate XVII, fig. 1).—The beds below the Ostrea bed are much thicker to the north of the Waipara River, and are well exposed in Birch Hollow, at the upper end of the high terraces, where they form two large bluffs. They consist of a lower series of rotted conglomerates, 50 ft. thick; a middle lignite series of grey sands and carbonaceous shales, in places passing into lignite-seams, together about 100 ft. thick; and a higher series of yellow sands with ironstone partings, about 150 ft. thick. The Ostrea beds consist of a lower oyster-bed, 15-ft. thick, separated from a high similar bed, 1 ft. thick, by 20 ft. of sandstone. They contain Ostrea sp. cf. dichotoma Bayle and Pecten hectori Woods. The beds here are flatter than in the Waipara River, and strike north-north-east, with a dip of 15° east-south-east. Weka Creek.—The Ostrea beds are well displayed in the Weka Creek, where they are about 40 ft. thick. At this locality I collected the specimens of Ostrea sp. cf. dichotoma Bayle figured by Woods, and he determined also Pecten (Camptonectes) hectori Woods from McKay's earlier collection. There are few other molluscs, but a fragment of a rhynchonellid was observed. The underlying rocks consist of loose white sands, 40 ft. thick, resting on 5 ft. of coal-shale, which here lies hard on the rotted argillite, and laterally dovetails into the sands. The Ostrea bed is again seen as a thin band in the northern tributary of Weka Creek rising near Waikare, and may extend some distance to the north-west in the Waikare-Hawarden district. East of the Weka Pass these lower beds have not been observed, and they are certainly absent at the eastern end of the district. “Saurian Beds” and Waipara Greensands. Waipara River.—An almost complete section of the beds between the Ostrea bed and the base of the Amuri limestone is exposed in the banks of the Waipara River between the Doctor's Gorge and the limestone gorge (Plate XVI). They consist of sands, mudstones, and greensands, and may be conveniently termed the “sulphur sands” and “sulphur mudstones,” together constituting the “saurian beds,” and the “Waipara greensands.” The sulphur sands and mudstones are so termed from the presence of a yellow efflorescence on the rocks, formed of sulphur compounds, combined with a distinct smell of sulphurous gases in the near vicinity of the cliffs and talus, particularly where these rocks are cut through by narrow gorges. The yellow efflorescence has not been chemically examined in the Waipara district, but a similar efflorescence on Clarentian mudstones in the Nidd Valley, near Coverham, has been reported on by the Dominion Analyst, who states,