388 Transactions. — Geology. 



in some of the high precipitous rock-faces. A notable ex- 

 ample is seen on the south-west side of Tank Gully, where 

 the strata forming the summit of the ridge have been sheared 

 along a nearly horizontal thrust-plane for some 17 ft., thus 

 displacing them relatively to the strata below to that amount. 



The strike of the beds on the north side of Tank Gully is 

 N.E.-S.W., and the dip N.W. at very high angles, which are 

 seldom under 80°. On the south side the strike is the same, 

 and the dip S.E. at angles varying from 60° to 75°. 



Mr. McKay, in 1877, examined this locality and noted the 

 N.W. and N.E. dips, but he apparently failed to recognise 

 the anticlinal arrangement of the beds.* In a section across 

 Tank Gully he shows the dips correctly ; but he marks the 

 beds on the N.W. side of the anticline as Trias and those on 

 the N.E. side as Carboniferous (Eimutaka series), and extends 

 the latter in his sketch so as to pass unconformably below the 

 former. It is noteworthy, however, that his description of 

 the strata in Tank Gully does not correspond with his 

 section. 



The plant beds are succeeded by a series of greyish and 

 greenish sandstones, slaty shales, and claystones. The shales 

 and sandstones alternate both in thin iamiuEe and in thick 

 beds. The greenish sandstones are generally highly indurated, 

 and weather to a greyish colour on exposed surfaces. They 

 are of all degrees of texture from fine-grained, which predomi- 

 nate, to coarse and gritty. They occasionally become pebbly,, 

 and pass into thin beds of sandstone conglomerate. In a 

 few places the finer-grained sandstones are brecciated with 

 small angular fragments of black claystone scattered spar- 

 ingly through a thickness of a few feet. 



The sandstones and claystones between Tank Gully and 

 Eocky Gully are interbedded with a few beds of red slaty 

 shale and a bed of pale-green aphanitic sandstone, which is 

 often streaked with thin interlacing veins of white quartz. 



Sir Julius von Haast, in 1861, examined the upper Eangi- 

 tata,f and on that occasion discovered the fossiliferous beds in 

 Eocky Gully. He subsequently revisited the same locality, in 

 1812,1 and made a collection of marine shells and saurian 

 bones, the latter including a number of vertebrae, one of 

 which was referred by Sir James Hector to the genus 

 Ichthyosatirus.% At the same time a collection of plant- 

 remains was made at Tank Gully. 



In his collection from Eocky Gully Sir Julius von Haast 

 reported the occurrence of OrtJiis, Productus, Atrypa, and 



♦ Reps. Geol. Expl., 1877-78, p. 94. 



t Von Haast, " Geology of Canterbury and Westlaud," 1878, p. '268. 



* Reps. Geol. Expl., 187'2-73, p. 1. 



§ Trans, N.Z. Inst., vol. vi., p. 334, 



