Speight. — Redcliff Gully, Rakaia River. 341 



wliicli cau be observed in other parts of Canterbury, notably in the Tre- 

 lissick basin at Castle Hill, distant sixteen miles to the north-east. Their 

 elevation — fully 2,000 ft. above similar beds at the Curiosity Shop, three 

 miles below the Gorge Bridge — implies that a considerable amount of 

 differential elevation has taken place in the central parts of the Southern 

 Alps, a fact which is also confirmed by a consideration of the Trelissick 

 basin. This elevation, taken in conjunction with the slight folding which 

 the beds exhibit, shows that the movements which formed these mountains 

 had not ceased in late Tertiary times, although, judging from the absence 

 of earthquakes associated with the chain, they have apjiarently ceased by 

 now. 



One statement of Captain Hutton's should not be passed over without 

 comment — viz., that the mound in the bed of the Rakaia known as Castle 

 Rock is composed of limestone. Although a casual examination of it from 

 a distance, especially as it is coloured slightly red in places, suggests that 

 it may be a fragment of the Redcliff limestone, a close examination of it 

 shows that it is entirely composed of greywacke and slaty shale, with a 

 strike a little south of east and a vertical dip. The rock is only 10 chains 

 long, and from 3 to 4 chains wide, and about 25 ft. raised above the river- 

 bed, so that there can be little doubt that a mistake has been made. No 

 other rocks could be seen in the river-bed to which Captain Hutton's 

 description could apply. 



His argument as to the erosion of our valleys in pre-Tertiary times, 

 as based upon this evidence, must therefore be taken with a considerable 

 amount of reservation. At the same time, it must be admitted that the 

 surface of the Alps had suffered erosion before the end of the Cretaceous 

 period, and that during a subsequent time of depression the sea invaded the 

 inlets thus formed, and portions of the marine beds then laid down were, 

 in specially favourable localities, preserved from the erosion of glaciers and 

 other denuding agents. Whether faulting has contributed to the preser- 

 vation of these beds is still an open question as far as Canterbury is con- 

 cerned. It must be admitted that a strong case can be made out in 

 regard to the Trelissick basin, but the Redcliff outlier furnishes none, as far 

 as my own observations go. 



Further, there is no sign in the conjunction of beds of dissimilar litho- 

 logical character, or in the landscape features, that any major line of faulting 

 occurs connecting the Trelissick basin and Redcliff Gully. The former 

 is a basin the result of folding, or prehaps a senkungsfeld, but it is quite 

 isolated, and surrounded on the western and south-western sides by the 

 uniformly high (between 6,000 ft. and 7,000 ft.) Craigieburn Mountains, 

 in which there is no notch or other landscape peculiarity demanded by such 

 an earth-movement as one accounting for the simultaneous formation of 

 both of these limestone outliers would necessarily require. 



