360 A. p. COLEMAN — GLACIAL PERIODS AND GEOLOGICAL THEORIES 



has been scanned with this in view. In India most references to the 

 Talchir and Salt range are brief and not detailed, so that little informa- 

 tion as to interglacial beds is to be expected. The published sections also 

 give little evidence in favor of a removal and readvance of the ice-sheets ; 

 but Mr Lydekker mentions the fact that there are several boulder beds at 

 different horizons/^ and it may be that observers have not recognized the 

 importance of noting stratified beds between the sheets of boulder clay. 



In Australia Professor David has given an extraordinary section from 

 the Bacchus Marsh district in Victoria, in which there are no less than a 

 dozen beds of "glacial mud stones," separated by stratified materials, 

 chiefly sandstone and conglomerate, the whole series being 2,000 feet 

 thick. In New South "Wales also a group of Coal measures, over 230 feet 

 thick and comprising from 20 to 40 feet in thickness of coal (the Greta 

 Coal measures), is sandwiched in between the erratic-bearing horizon of 

 the Lower Marine series and the similar horizon of the Upper Marine 

 series."* 



In South Africa the southern Dwyka is often very thick, 1,000 or 1,300 

 feet, and includes much interstratified shale or sandstone or conglomerate, 

 clearly of an interglacial nature ; but little attention has been paid to this 

 feature, and, so far as I am aware, no attempt has been made to follow up 

 these interglacial deposits so as to indicate the extent of the retreat of the 

 ice-sheet. Doctor Molengraaff mentions the stratified deposits between 

 the sheets of tillite and suggests that there was a periodical forward and 

 backward movement of the ice, but evidently looks on these movements as 

 of small extent at the borders of the ice-sheet."" Mr Eogers describes a 

 conglomerate pavement in which a second advance of the ice has smoothed 

 and scratched the blocks in a lower tillite 50 to 80 feet thick, and states 

 that there is some stratified shale without pebbles interbedded with the 

 conglomerate."^ 



From my own observations it may be stated that stratified materials 

 occur within the Dwyka at several places in South Africa, sometimes in 

 beds of considerable thickness. Important beds of sandstone occur in 

 Cape Colony near Matjesfontein, and near Laingsburg also the section of 

 Dwyka, standing nearly vertical, shows at the bottom a thick layer with 

 many boulders, followed by 150 or 200 feet of shale, well stratified and 

 with no large stones, and then another thick bed of unstratified tillite. 



" Journal of the Geological Society of London, vol. xlii, p. 261. 



" Ibid., vol. Hi, 1896, p. 300. 



»5 Geology of the Transvaal, p. 71. 



" Geology of Cape Colony, pp. 162-164. 



