354 A. p. COLEMAN GLACIAL PERIODS AND GEOLOGICAL THEORIES 



cessful in tracing these early Paleozoic boulder clays on the Mount Lofty 

 ranges in South Australia. He iinds them extending 460 miles from 

 north to south and 250 from east to west, with a thickness of 1,500 feet. 

 Many well striated stones have been obtained from this tillite, which is 

 supposed to have been formed by floating ice at sealevel.^® The general 

 question of Cambrian boulder clays is discussed by Professor David also, 

 who suggests that the ice reached sealevel, on the evidence of intercalated 

 beds of limestone with what are probably radiolarian shells. The direc- 

 tion of motion was probably from south to north, as shown by inclosed 

 boulders.^^ The Cambrian boulder clay is found also on the west coast 

 of Tasmania. No striated rock surfaces have been reported beneath the 

 Cambrian tillite. • 



The South African early Cambrian or late pre-Cambrian tillite, be- 

 longing to the Griquatown series in Cape Colony, has been examined by 

 Mr Eogers and his assistants and is known to cover at least 1,000 square 

 miles.^° Some scratched pebbles sent me by the kindness of Mr Rogers 

 are typically glacial. 



The South African Cambrian tillite occurs in about latitude 29°, while 

 that of Australia ranges through several degrees of latitude, from Tas- 

 mania to latitude 33° or 33°, in South Australia; so that ice action 

 reached considerably nearer to the equator than in the Pleistocene glacial 

 period, but falls much behind the Permo-Carboniferous in this respect. 



In North America there are many instances of coarse conglomerates 

 which might be glacial in the Lower Cambrian, or what is probably its 

 equivalent, the Keweenawan; but, so far as my reading goes, only one 

 authority has found striated stones in the boulder conglomerates. Doctor 

 Bell reports boulders reaching diameters of 3 feet 8 inches, having grooves 

 like glacial striae, in a conglomerate with sandy matrix belonging to the 

 Keweenawan of Pointe aiix Mines, near the southeast end of lake Supe- 

 rior.^^ Messrs Lane and Seaman describe a Lower Keweenawan conglom- 

 erate as containing "a wide variety of pebbles and large boulders, in struc- 

 ture at times suggestive of till," from the south shore of lake Superior.^- 



"^ Royal Society of South Australia, vol. xxx, p. 227 ; also American Association for 

 the Advancement of Science, 1902, pp. 190-204 ; and Nature, December 19, 1907, p. 165. 

 (Report of Geological Surve.v of South Australia.) 



^ Australian Association for the Advancement of Science, 1902, pp. 199-200. 



^ Transactions of the Geological Society of South Africa, vol. ix, 1906 : The Campbell 

 Hand and Griquatown series in Hay., by Rogers, pp. 8 and 9 ; also Transactions of the 

 Australian Association for the Advancement of Science, 1906, paper 24, The Glacial 

 beds in the Griquatown series ; and by Schwartz, Journal of Geology, vol. xiv, no. 8, pp. 

 683-691. 



=1 Geology of Canada, 1876-1877, p. 214. 



^ Journal of Geology, vol. xv, no. 7, p. 688. 



