Thomson.^ — Geology of Middle Waipara and Weka Pass District. 34:3 



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) 

 hector i 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 speci- 

 mens 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 V/aikare, and may extend some distance to the 



north-west m 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 Crorge and the limestone gorge 

 (Plate XVI). They consist of sands, mudstones, and greensands, and may 

 bCj 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 

 efilorescence 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 dis- 

 trict, but a similar efflorescence on Clarentian mudstones in the Nidd Valley, 

 near Coverham, has been reported on by the Dominion Analyst, who states, 



