Thomson. — iitoloijij of 'Middle Clartncc and lire VaUeys. 301 



bv tlie differential uplifts which gave rise to the great Marlborough con- 

 glomerate must have been in large part destroyed by the subsequent 

 drowning during the deposition of the marine (Awatere ?) beds which follow 

 the conglomerate. The greater part of the present drainage-pattern appears 

 to be consequent on the later, more intense, deformations. This part 

 includes the Middle Clarence Valley, occu]\ving the tectonic depression 

 between the two mountain blocks, and the numerous large streams entering 

 it on both sides nearly at right angles. The course of the Lower Clarence 

 River in the gorge, however, demands a different explanation. 



The Clarence River on leaving the middle valley bends at a right 

 angle, and passes between the north-eastern end of the Looker-on Range 

 and the Sawtooth Range in a rock-bound gorge nearly 4,000 ft. in depth, 

 cut through the pre-Notocene rocks. This bend, as Cotton (1913) has shown, 

 is not an elbow of capture, since there is no gap by which the Clarence 

 could have had its outlet before the hypothetical capture, nor have other 

 eastward-flowing streams made any appreciable progress in breaching the 

 continuous wall of the Looker-on Range. This part of the river-course 

 must tlierefore be a survival of an older system of drainage, the river 

 cutting down a gorge as the mountains rose. 



The Notocene rocks are found at no great distance apart on each side 

 of the range at this point, and it is practically certain that the oldermass 

 was here completely submerged during the later Notocene, so that any 

 pre-existing drainage must have been completely destroyed. The course 

 of the river through the mountains cannot, therefore, be antecedent in 

 the sense of a relict of a pattern existing on an emergent portion of the 

 oldermass during the main Notocene depression. It must be explained, 

 therefore, as an anteconsequent course (c/. Cotton, 1917, p. 253) — i.e., a 

 course established during the early stages of the deformation. 



The great development of the great Marlborough conglomerate in the 

 area between Kekerangu and the Lower Clarence demands the assump- 

 tion of local differential movements in this area as well as over the site of 

 the Kaikoura Range, but the mountains then formed may have lain either 

 on the site of the Sawtooth and Looker-on Ranges or seaward of the pre- 

 sent coa.st-line near Kekerangu. The latter is the more probable, since the 

 Sawtooth Range is flanked on the south-eastern side by Clarentian rocks, 

 followed by the Amuri limestone in the Lady Range, which would not be 

 the case if the material of the conglomerate were derived from an uplifted 

 block on this side. The elevation of the Sawtooth Range, then, appears 

 to be due to the anticlinal folding of the later deformations. Prior to these 

 more intense movements one must assume an even or slightly differential 

 uplift after the deposition of the marine beds following the conglomerate, 

 with the formation of a coastal plain sloping to the south-east. On this 

 plain consequent rivers draining south-east became established, and one of 

 these persisted through the later deformations as the lower course of the 

 Clarence River. Probably this anteconsequent drainage removed the greater 

 part of the softer marine beds overlying the conglomerate, so that when 

 the later faulting took place the former were preserved only in the Bluff 

 River and from Deadman's Creek southwards. 



The Kaikoura and Looker-on Ranges probably did not escape Noto- 

 pleistocene glaciation, but its effects have probably been destroyed by the 

 heavy subaerial erosion which followed, since there is no evidence to show 

 that the Middle Clarence Valley was ever occupied by a glacier, while the 

 mountains themselves, so far as explored, now exhibit only the work of 



