Park. — Geological History of Eastern Marlborough. 65 



Art. VIII. — The Geological History of Eastern Marlborough. 



By Professor James Park, F.G.S., F.N.Z.Inst. 



[Read before the Otago Institute, 9th November, 1920 ; received by Editor, 31st December, 



1920 ; issued separately, 27th June, 1921.] 



Contents. p age 



Introduction . . . . . . . . . . 65 



A Question of Nomenclature . . . . . . . . 66 



Synopsis . . . . . . . . . . . . 67 



Geological History . . . . . . . . . . 67 



The Post-Miocene Conglomerate . . . . . . 68 



Relationship of Post-Miocene Conglomerate to Underlying Tertiary 



Formations . . . . . . . . . . 69 



Involvement of Post-Miocene Conglomerate . . . . 70 



Newer Pliocene . . . . . . . . . . 71 



Conclusion .. .. .. .. .. .. ..71 



Introduction. 



In two papers, published in 1917 and 1919, Dr. J. Allan Thomson champions 

 the views of Dr. C. A. Cotton (1913, 1914a, and 1914b) as to the genesis 

 of the physiographic features of eastern Marlborough and origin of the so- 

 called post-Miocene conglomerate. In the last of these papers he restates 

 at great length the observations of McKay made in 1886, 1890, and 1892, 

 and the opinions of Cotton, and disagrees with my view that the post- 

 Miocene conglomerate is morainic. With the zeal of an advocate he con- 

 tends that my " hypothesis involves the formation of the great Clarence 

 and other faults in the late Notopleistocene, and is quite untenable." 

 Why untenable ? Geophysicists recognize that the crust of the earth will 

 be subject to tensional stresses, fracturing, and faulting so long as the 

 denudation of mountain -chains and the piling-up of sediments on the sea- 

 floor continue. 



The view I have always maintained is that the Clarence fault is of 

 considerable antiquity, and that the involvement of the glacial and older 

 strata was caused by a revival of movement along the old fault-plane. 

 Great faults are of slow growth. 



As if doubtful of warranty for his extreme pronouncement, Thomson 

 adds, " In any case, the evidence for the fluviatile origin of the lower beds 

 of the series is overwhelming." But even if partly fluviatile, this would 

 not invalidate my view that the great conglomerate is morainic. There 

 are moraines and moraines. The morainic matter carried on the back of 

 a glacier invariably consists of a tumbled pile of angular blocks of rock. 

 In such a deposit fluviatile material is usually absent. Curiously enough, 

 this appears to be the only type of moraine that Thomson recognizes as 

 undeniably glacial. But terminal moraines, of which we have in New 

 Zealand many fine examples, both ancient and modern, are invariably 

 composed of fluviatile drifts mingled to a greater or less extent with 

 tumbled ice-carried blocks. 



During the past two years I have attempted to determine the relative 

 proportions of fluviatile drift and tumbled blocks in some well-known 

 terminal moraines in Otago and Southland, and I may say that the task 

 proved more difficult than I anticipated. The results obtained I can only 

 claim to be rude approximations, but they are sufficiently near the truth 



3— Trans. 



