iNTERGLACtAL PERIODS IN ANCIENT ICE AGES 361 



Some irregular masses of sandy conglomerate occur in the boulder clay 

 also. 



Near Vereeniging, in Transvaal, there is an apparently interglacial bed 

 of sandstone including a small seam of coal with a thick bed of boulder 

 clay beneath and a thin sheet of conglomerate above, but there is some 

 doubt as to the glacial nature of the upper conglomerate. It may be 

 water formed, recomposed of stones from the tillite beneath. 



At N'gotsche mountain, in northeastern Natal, the Dwyka is 480 feet 

 thick and includes in the upper part two thin beds of shale, and still 

 higher a quite thick interglacial sandstone, above which is a fairly thick 

 bed of sandy tillite with many boulders. 



The succession of boulder clays and stratified shale and sandstone or 

 conglomerate seen at some points in South Africa matches well the section 

 of boulder clay and interbedded clay and sand of the Pleistocene inter- 

 glacial section at Scarboro, near Toronto, and probably represents a 

 similar series of events, though no fossils were observed in the African 

 deposits to give indications of changes of climate. That there are inter- 

 glacial beds of great thickness, implying a considerable lapse of time, in 

 the Dwyka can be stated with certainty; but how completely the ice was 

 removed in these interglacial periods is doubtful, because of the small 

 amount of evidence available. 



There were at least local interglacial stages in all three continents dur- 

 ing the Permo-Carboniferous ice age, but whether these interglacial stages 

 covered the whole of each area or coincided in the different continents 

 must remain problematic. 



As to the early Cambrian ice age there seems little evidence at hand 

 either in favor of or against interglacial periods, except in Australia, 

 where fossiliferous limestone is reported from between layers of tillite by 

 Professor David. 



The Lower Huronian boulder conglomerate, about 500 feet thick, at 

 Cobalt has stratified slaty beds between unstratified beds of graywacke 

 with angular and subangular boulders. Above the Lower Huronian comes 

 a Middle Huronian conglomerate, sometimes boulder-bearing, which may 

 represent a recurrence of glacial conditions, but no striated stones are 

 known from it, perhaps because they have not been looked for. 



In general it may be stated that interglacial stratified deposits free 

 from boulders, indicating at least local changes of climate, are known 

 from all of the glacial periods ; but these have not been followed up suffi- 

 ciently to judge of their universality in the older periods. In the Pleis- 

 tocene ice age of North America there is proof of at least one complete 



