236 HISTORY OF GEOLOGY AND PALEONTOLOGY. 



transported by ice, and a similar explanation was suggested 

 for the exotic blocks in the Alpine and Carpathian " Flysch " 

 formation. From time to time examples of boulder and 

 conglomerate deposits were reported and were dealt with in 

 this way. To mention a few examples: in 1870 Sutherland 

 described breccias with polished blocks in the Karroo Beds of 

 South Africa, and in his explanation of them as glacial in 

 origin he was supported by Griesbach (1871) and Stapff 

 (1899); in Australia, R. D. Oldham explained boulder con- 

 glomerates in Carboniferous and Permian time as material 

 transported and stranded by icebergs; Waagen (1887) de- 

 scribed scratched pebbles and polished blocks from the Salt 

 Range in the Punjab, and referred them to a Carboniferous 

 Ice Age; Notling more recently (1896) concludes they belong 

 to a Permian Ice Age ; Sir A. Geikie mentioned glacial traces 

 in the Cambrian rocks of Scotland, and Reusch (1891) in the 

 Cambrian deposits of Northern Norway. The conclusion 

 drawn by James Geikie and James Croll is that all the greater 

 epochs in the history of the earth have been marked by a 

 series of glacial and interglacial episodes. 



But the number of geologists who accept the teaching of 

 repeated glaciation of wide territories is rather decreasing than 

 increasing. The minute detail in which geological maps are 

 now being prepared tends to show that in many cases all these 

 phenomena of scratched pebbles, and boulders, and polished 

 surfaces may be observed in the sheared and brecciated rock- 

 material occurring along the planes of great crust-movements. 

 And in no case will a cautious geologist be willing to accept 

 an ice age, or even local glacial action, in a remote geological 

 epoch as the explanation of scratched pebbles and the occur- 

 rence of exotic boulders, unless he be in a position to investigate 

 the matter for himself, or it can be conclusively proved to him 

 that there has been no history of crust-disturbance. The 

 attitude of present-day geology with respect to the much 

 vexed questions of glacial action is to hold an open mind 

 towards each alleged example. 



The Pleistocene ice-mantle had its chief distribution in the 

 north-west of Europe and in the north-east of America ; but, 

 with the exception of those large areas covered by inland ice, 

 the evidence of glaciers is found only in mountain ranges 

 which still possess glaciers, or in which a very slight climatic 

 depression would call forth glaciers. Hence the glaciation 



