Speight. — Physiogra'phy of the Cass District. 147 



due to the modification of such a basin by stream and glacier action. 

 The location of the station affords ample (tpportunity for the investigation 

 on a minute scale of many of the earth-features produced under such 

 circumstances, and it is to be hoped that these will be undertaken as a 

 corollary to the biological investigation for which the station was primarily 

 established. 



The rocks of the neighbourhood consist entirely of folded greywackes, 

 slaty shales, and related sedimentaries of Trias-Jura age, which may be 

 looked on as formed principally from the debris of an ancient granite land 

 lying either to the east or to the west of the present land which constitutes 

 the islands of New Zealand. In places the rocks contain much silica, and 

 become cherty or jasperoid in character, as can well be seen on the hill 

 to the north-west of Lake Sarah, near the Cass Railway-station. The 

 quartzose nature of the rock is so marked at this spot that at one time it was 

 prospected for gold by West Coast miners, and their shafts are still visible 

 on the western end of the hill ; no payable gold was encountered. The 

 general strike of the beds as disclosed in the railway and road cuttings is 

 N.E.-S.W., but considerable variations in the direction occur within short 

 distances. The dip of the beds is usually at high angles, the result of 

 folding by powerful earth-pri^ssures operating in a S.E.-N.W. direction, 

 these movements having been attended by faulting, as can be seen from 

 the smoothed and slickensided surfaces exposed at times in the cuttings. 

 A most important feature, which has resulted largely from the same cause 

 as the folding and faulting, is the system of joints which penetrate the rocks 

 and render them especially susceptible to disintegrating agencies, such as 

 frost, under whose influence they break into rectangular fragments and 

 furnish the enormous supply of waste which mantles the mountains in the 

 vicinity, and which gradually moves downward to lower levels, supplies the 

 material for fans, and at times impedes and clogs the normal course of 

 streams. 



The rocks are not known to contain fossils, although remains of molluscs 

 have been reported from the road-cuttings on the Waimakariri front ; but 

 they have been assigned to the Trias-Jura age, from their continuity 

 with, and lithological similarity to, rocks occurring at Mount Potts, on the 

 Rangitata, at Malvern Hills, and at the Clent Hills, which contain plant 

 fossils of undoubted Lower Jm'assic age. 



The date at which they were folded was probably Late Jurassic or Early 

 Cretaceous, since rocks of more recent age than this are not affected to the 

 same extent, although they, too, have experienced a moderate degree of de- 

 formation, showing that folding m')vements had not entirely ceased at that 

 date. When they were folded a mountain range was probably formed which 

 was base-levelled subsequently by stream or sea action, and on the surface 

 thus produced Tertiary limestones, sandstones, &c., were laid down, such as 

 can now be seen at Castle Hill, forming in all probability a discontinuous 

 sheet over the area. The region was then raised with its veneer of later 

 sediments, with some amount of differential movement and faulting, which 

 resulted in the formation of such intermontane basins as at Castle Hill 

 and the mid- Waimakariri. The tract was then dissected by stream action, 

 which had advanced to an early mature stage when it was subjected to a 

 somewhat severe glaciation. The agency of ice and the subsequent results 

 of the formation of waste by the action of frost on the jointed sedimentaries 

 have been responsible, either directly or indirectly, for its more distinctive 

 landscape features. 



