Park. — Geological History of Eastern Marlborough. 71 



Newer Pltocene. 



As a further consequence of the pivotal (or differential) elevation, the 

 refrigeration which afterwards culminated in the glaciation of a large part 

 of the South Island and a small part of the North Island began in Otago 

 and Southland as far back as the early Pliocene, and in Marlborough in 

 the late Pliocene. The general advance of the alpine glaciers began 

 in the late Pliocene, and throughout the South Island this was a period 

 of intense fluviatile activity. In the early Pleistocene the high Kaikoura 

 chains were covered with permanent ice-fields that fed the Clarence glacier, 

 the terminal face of which reached the sea at the time of maximum 

 refrigeration. 



It was during the early Pleistocene that the Marlborough fluvio-glacial 

 conglomerate was deposited. The piling-up of from 4,000 ft. to 12.000 ft. 

 of sediments and other rocky detritus on the floor of the Clarence Valley 

 disturbed the isostatic condition of the crustal strip lying along the Clarence 

 fault, and as a result of this disturbance there was a revival of movement 

 along the old fault-plane. McKay reported in 1886 that a distinct depres- 

 sion marked the line of the great fault, and this depression was said by 

 the settlers to have been formed by the historic earthquake of 1855, which 

 is also known to have opened gigantic earth-rents in other parts of Marl- 

 borough, as well as in Wellington. 



I would suggest that it was the overloading of the Clarence segment 

 which caused the Inland Kaikoura chain to creep towards the south-west. 

 This and crustal weakness originated the overthrust which eventually 

 entangled the Cretaceous and Tertiary strata and post-Miocene conglome- 

 rate along the course of the Clarence fault. But this suggestion is purely 

 hypothetical and incapable of proof. 



Conclusion. 



Herbert Spencer has laid it down in his First Principles that no hypothesis 

 is capable of more than partial proof, and that of two rival hypotheses the 

 one that approaches nearest the truth is that which does least violence to 

 fundamental principles. I venture to think that Cotton's titanic faulting 

 and stupendous walls of weak, unconsolidated sediments (vide fig. 2, Cotton, 

 1913) postulate conditions that appear almost impossible. Moreover, his 

 and Thomson's contention that the post-Miocene conglomerate is conform- 

 able to the " grey marls," notwithstanding that it is composed of material 

 derived from all the underlying formations, is opposed to all the canons 

 of stratigraphical geology. The view of conformity did not even suggest 

 itself to Hector, McKay, or myself. 



According to Cotton's hypothesis, the faulting was a single catastrophic 

 movement of such magnitude as to expose the Tertiary and Cretaceous 

 strata in a stupendous fault-scarp from the steep face of which blocks and 

 vast slabs of the different beds, under the influence of gravity, fell or slid 

 into the valley below, forming the " pell-mell " so well described by McKay. 

 But the blocks are contained in a matrix of fluviatile drift composed 

 mainly of the basement Juro-Triassic rocks. Evidently the Clarence Valley 

 was already drained by a well-established river-system. It seems incredible 

 that the titanic dislocation required by Cotton's view could have taken 

 place without causing serious disarrangement of the pre-existing drainage- 

 system. 



If it be conceivable that the faulting proceeded by a series of catastrophic- 

 displacements that exposed in a steep escarpment first the Tertiary and 



