THE ICE AGE AND ITS WORK. 285 



the Viiriuus groups of mountains, Avhile it is liopelessly impossible to 

 explain them on any theory of h^cal glaciers, even with the aid of sub- 

 mergence and of floating' ice. - - - 



The center of the great glacier sheet of North Wales api)earsto have 

 been over the Arenig Mountains, whence erratics of a peculiar volcanic 

 rock have been traced to the north and east, mingling with the last- 

 described group ; while a distinct train of these Welsh erratics stretches 

 southeastward to the country west of Birmingham. 



In the Isle of Man are found many erratics from Galloway and a few 

 from the Lake District. But th(» most remarkable are those of a very 

 peculiar rock found only on Ailsa Craig, a small island in the Frith of 

 Clyde, and a single bowlder of a peculiar i)itchstone found only in the 

 Isle of Arran. The Ailsa Craig rock has also been found at Moel Try- 

 faen, on the west side of Snow don, and more recently at Killiney County, 

 Dublin, on the seashore.* 



The case of the bowlders in the Isle of Man, wiiicli have been carried 

 nearly 800 feet above their source, has already been mentioned, but 

 there are many other examples of this phenomenon in our islands; and 

 as they are of great importance in regard to the general theory of glacial 

 motion, a few of them may be noted here. So early as 181 8 Mr. Weaver 

 described a granite block on the top of Cronebane, a slate hill in Ireland, 

 and several hundred feet higher than any place where similar granite 

 was to be found in siin; and he also noticed several deposits of lime- 

 stone gravel in places from 300 to 400 feet higher than the beds of lime- 

 stone rock, which are from 2 to 10 miles off. Debris of red sandstone is 

 also found much higher than the parent rock. Bowlders of Shap gran- 

 ite, Mr. Kendal tells us, have passed over Stainmoor by tens of thou- 

 sands, and in doing so have been carried about 200 feet above their 

 source; and the curious Permian rock, "Brockram," has been carried 

 in the same direction no less than 1,000 feet higher than its higluist 

 point of origin. t In Scandinavia there are still more striking examples, 

 erratic blocks having been found at an elevation ot 4,500 feet, which 

 could not possibly have come from any place higher than 1,800 feet.t 

 We thus find clear and absolute demonstration of glacier ice moving 

 u})hill and dragging with it rocks from lower levels to elevations vary- 

 ing from 200 to 2,700 feet above their origin. In Switzerland we have 

 proof of the same general fact in the terminal moraine of the northern 

 branch of the Rhone glacier being about 200 feet higher than the Lake 

 of Geneva, with very much higher intervening ground. - - - 



The facts thus established render it more easy for us to accept one 

 of the latest conclusions of British glacialists, A great submergence 

 of a large portion of the British Isles during the glacial period, or in 

 the interval between successive phases of the glacial period, has long 



• Nature, March 16, 1893; voI.xlvii, p. 464. 

 t Wright's Man and the Glacial Period, p. 154. 

 IJames Geikie's Great Ice Age, 2d ed., p. 404. 



