292 THE CLIMATIC FACTOR AS ILLUSTRATED IN ARID AMERICA. 



scratched boulders placed the question beyond doul)t. This culminating; evidence was obtained, 

 in the first instance, at Petersburg (on the Northern Railway from Adelaide) in 1901, and was sub- 

 sequently confirmed during a visit to the same place by Professor T. W. E. David, F.R.S., Mr. E. F. 

 Pittman, the Government Geologist of New South Wales, and myself. In association with those 

 two experienced geologists, fifteen glaciated stones were obtained during a search of two hours. 



"The erratics are frequently facetted, as well as striated, under ice-action. The striae vary in 

 depth and direction on the same face, and are often as distinct and fresh-looking as those which occur 

 on the stones of the Pleistocene Boulder-Clay " (1908: 2.39-41). [The area of tillitc accumulation] 

 "was prol;)ably bounded on the south and west by moderate highlands, consisting of pre-Cambrian 

 (Algonkian) quartzites, schists, limestones, and other sediments with exposed igneous batholiths 

 and dikes of varied types. The pre-Cambrian complex had been subjected to gioat waste and was 

 probably in the form of subdued relief at the time of the Cambrian glaciation. Remnants of this 

 pre-Cambrian continent are found in the geological axes of the Mount Lofty ranges, Yorke Peninsula, 

 and Kangaroo Island; the crystalline ranges of Eyre Peninsula, the porphyrite outcrops of the 

 Gawler ranges, and the igneous and metamorphic plateau of Western Australia. 



"In no instance has a glaciated floor been observed, the occurrence of which would suggest 

 the probability of ice-action above sea-level. The absence of such an ice-marked floor, over the 

 area in question, is not, however, to be wondered at when in no case have the glacial deposits 

 been discovered in contact with a pre-Cambrian surface. The Cambrian till is found resting 

 conformably on laminated quartzites in an orderly succession, and while the junction l)etween 

 the respective beds is always sharp and decided, it seems moderatelj' certain that the glacial 

 d6bris was laid down on a floor of contemporary marine deposits — in which case the agent of 

 distribution must have been floating ice. This view is supported by the fact that the glacial 

 material forms, practically, one continuous sheet, spread over an immense extent of country, and 

 maintains a remarkable uniformity as to thickness, lithological characteristics, and types of 

 erratics throughout its entire extent. At the same time it is very probable that the ice-field was 

 at no great distance from this area of deposit" (1912: 197-8). 



The following will make it clear that in all probability there is a great time hiatus without 

 mountain-making movements between the Lower Cambric and the tillite. 



In the Onkaparinga Valley, about 20 miles south of Adelaide, a Lower Cambric impure lime- 

 stone rests sharply and wiOiout transition on a series of tillite beds here 570 feet thick, separated 

 by two thin quartzite zones together having a thickness of 22 feet. 



In the Sturt Valley section, a few miles south of Adelaide, may also be seen the contact between 

 the Lower Cambric and the tillite. Here also the basal Cambric bed is an impure dolomitic 

 limestone 4 feet thick, which without transition rests "immediately upon characteristic till" 

 (1908: 251), here nearly 800 feet thick. 



In the Appila-Gorge section the tillite upper boundary "is marked by a sharp line of division, 

 in which boulder-clay with big erratics is covered by a homogeneous fissile slate or shale" (253). 

 The tillite is here about 1,526 feet thick, divided into three divisions: "(a) An upper till of 120 

 feet; (6) an interbedded series of slates to 656 feet; and (c) a lower till of 750 feet" (253). 



In Norway, according to Strahan, 



"The sandstones occur in the most irregular manner and wedge in so suddenly as almost to 

 resemble included masses; they contain also fragments of shale more or less rolled, and in this 

 and other respects indicate that deposition alternated with erosion under the influence of varial)le 

 currents. * * * The Gaisa beds present only such features as are common to rocks of the 

 type of the Wealden, Trias, Coal Measures, or Old Red Sandstone, and give no hint of the action 

 of ice. But on visiting the section near Bigganjargga, referred to by Dr. Reusch, I found a deposit 

 of which I have seen no counterpart in any of those formations. * * * jn \\^q lowest ledge, 

 just above high-tide mark, a lenticular mass of darker rock [a tillite] intercalated between the 

 ledges of sandstone at once arrests the attention, even as seen from the deck of a steamer. 



"The mass itself is a boulder-rock quite unlike any of the Gaisa sandstones or conglomerates 

 which I saw elsewhere. It is referred to by Dr. Reusch as a conglomerate, but from the fact of 

 its being neither stratified nor waterworn I prefer to avoid the use of that term. It may be 

 described as a dark-bluish or ashy-grey friable rock, composed of a heterogeneous mixture of grit, 

 sand, and clay of all degrees of coarseness, and containing boulders ranging up to 2 feet in length 

 scattered through it. Though quite unstratified, it shows here and there a slight schistose 

 structure. The included boulders, which are of all shapes and lie at all angles, consist principally 

 of red and grey granites, and of quartz-grits resembling those of the Gaisa formation. I did not 

 succeed in finding any striated blocks, but the fact that the matrix has been hardened and adheres 



