Speight. — The Tertiary Beds of the Trelissick Basin. 



323 



conformable sequence. The whole area was then elevated with differential 

 movements, either of faulting or folding, or both combined, which resulted 

 in the formation of a basin-shaped hollow, some five miles by three, in 

 which the Tertiary sedimentaries were preserved from the active eroding 

 agents which removed the weaker beds from exposed positions either on 

 the elevated country in the neighbourhood or in the valleys more directly 

 subject to glacier and river erosion. In all probability the area was a snow- 

 field at the height of the glaciation ; but there is little sign of glacier action 

 in the area itself, except in the conchoidal hollows at high elevations in 

 the moimtains, where corrie glaciers probably nestled, and at the northern 

 and southern end of the basin, where the truncation and faceting of spurs 

 does suggest that glaciers invaded the area from the Waimakariri Valley 



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Fig. 1. — Geological sketch-map of the Castle Hill Basin. (Scale. 1 mile to £ in. approx.) 

 1, greywacke ; 2, sands, greensands. marls, &c. ; 3. tuff beds ; 4. limestone ; 

 5, sands, sandy clays, and shales — Pareora beds. 



on the north and the Kakaia on the south (Plate XXI, fig. 1). But this evi- 

 dence is not supported by the other signs of glaciation, such as lateral and 

 terminal moraines, rounded and scratched surfaces, roches moutonnees, &c, 

 and it is therefore possible that the truncation of the spurs may be due 

 to faulting and the facets may be fault scarps of recent origin. These 

 would be preserved at the ends of the spurs, while the course of the faults 

 across the intervening valleys would be masked by the rapid and enormous 

 accumulations of waste. 



11* 



