DYNAMICAL GEOLOGY. 235 



Numerous observations in different areas have testified to 

 the frequent oscillations of the glaciers during the Ice Age. 

 The glaciers appeared to have frequently retired, and ice-fields 

 to have diminished in size as often as any amelioration in 

 climatic conditions set in. Such variations may be observed 

 in ice-clad regions at the present day. And as the lique- 

 faction of the ice-masses gives rise to larger volumes of water, 

 the frequent local floods, of which evidences are afforded in 

 the intercalation of fluvio glacial deposits within the glacial 

 series, are thought to have been associated with periodic 

 oscillations. 



Two main advances of the mountain glaciers and of inland 

 ice were determined by Ramsay for the British Isles and by 

 Heer for the Alps, and have been confirmed by Scandinavian 

 and German geologists upon the evidence of the glacial and 

 fluvio-glacial deposits in their respective countries. In all 

 these areas a prolonged interlude of milder climatic conditions 

 appears to have intervened between two chief epochs of 

 glaciation. But Professor Penck in recent papers has aug- 

 mented the number of distinct epochs of glaciation in the 

 Alps and North Germany to three or four, thus approaching 

 the " five " glacial intervals enumerated by Professor James 

 Geikie, and the "seven" by James Croll. On the other 

 hand, Hoist in Norway, Upham and Wright in North America, 

 and many other authorities recognise only one Ice Age, marked 

 by occasional seasonal or periodic variations of no great 

 significance in the dimensions of the glaciers and inland ice. 



It is still more doubtful whether geologists have been right 

 in supposing that several Ice Ages occurred during geological 

 epochs previous to the Diluvial Age. Ramsay, in 1855, 

 explained certain Permian conglomerates in England as 

 accumulations transported by glacial action, and Dr. Blanford 

 applied a similar explanation in 1856 to the "Talchir" con- 

 glomerates of almost the same geological age in Central and 

 Southern India. It then became commonly accepted that 

 extensive glaciation had occurred in the Permian geological 

 epoch. Erratics and scratched pebbles have since been 

 described from the Silurian rocks in the southern counties of 

 Scotland by Moore and James Geikie, and also in the Old 

 Red Sandstones or Devonian rocks of Scotland by Ramsay. 



The Miocene conglomerates in the neighbourhood of Turin 

 were explained by Ramsay, Lyell, and Gastaldi as material 



