484 THE IGE AGE IN NORTH AMERICA. 



characteristic Lower Silurian fossils, in which are numerous 

 erratic blocks of gneiss and granite, some of them as many as 

 nine feet in length. Both Dr. Ramsay and Mr. James Geikie 

 believe that the nearest source from which these fragments 

 could come is one hundred miles or more to the north. Their 

 theory is that, in the early Silurian times, the region occu- 

 pied by the Hebrides and the adjoining coast of northern 

 Scotland consisted of an immense granitic mountain uplift, 

 down which glaciers descended to the sea, sending oif bowlder- 

 laden icebergs, which wandered to the vicinity of Ayrshire 

 and Wigtonshire, and there dropped their burdens. 



In India, also, according to Dr. Ramsay, Medlicott and 

 Blanford describe " old slates supposed to be Silurian, con- 

 taining bowlders in great numbers," which these experienced 

 authorities believe to be of glacial origin. They also de- 

 scribe other very ancient transition beds which overlie rocks 

 "marked by distinct glacial striations." Again, Dr. Ramsay 

 describes bowlder-beds in the south of Scotland, on the Lam- 

 mermoor Hills, south of Dunbar, which " contain what seem 

 to be indistinctly ice-scratched stones." These beds lie "un- 

 conformably on Lower Silurian strata," and are now gener- 

 ally believed by the members of the Geological Survey of 

 Scotland to be of glacial origin. Dr. Ramsay goes on to say : 



I know of no bowlder formations in the Carboniferous series, 

 but they are well known as occurring on a large scale in the 

 Permian brecciated conglomerates, where they consist of peb- 

 bles and large blocks of stone, generally angular, imbedded in 

 a marly paste ; . . . the fragments have mostly traveled from 

 a distance, apparently from the borders of Wales, and some of 

 them are three feet in diameter. Some of the stones are as 

 well scratched as those found in modern moraines or in the 

 ordinary bowlder-clay of what is commonly called the Glacial 

 epoch. In 1855 the old idea was still not unprevalent that 

 during the Permian epoch, and for long after, the globe had 

 not yet cooled sufficiently to allow of the climates of the exter- 

 nal world being universally affected by the constant radiation 

 of heat from its interior. For a long time, however, this idea 



