148 SUBMAKINE AND TEEEESTKIAL DKIFT. [Ch. XI. 



in the same direction. Their vast size also must often tend to give an 

 uniformity to their scoring action, over a space several miles in width. 

 Could we imagine buildings such as St. Peter's or St. Paul's to be 

 submerged, and an iceberg, several miles in diameter and two thou- 

 sand feet in height, advancing with the velocity of two or three miles 

 an hour to strike them, it is evident they must be thrown down as 

 readily as were the stone walls of the peasants' chalets in the early 

 part of the present century by the Gorner glacier above Zermatt. 

 "We may, therefore, fairly presume that whenever a submerged area 

 which had once been traversed by floating and occasionally strand- 

 ing icebergs is converted into land by upheaval, it will display on its 

 surface most of the characteristics which mark the former agency of 

 glaciers on dry land. No sharp pinnacles of rocks can be left stand- 

 ing, since they will all have been worn down and reduced to dome- 

 shaped masses, while scratches and long grooves will everywhere be 

 left on rocky surfaces. Even till, or unstratified matter, undistinguish- 

 able from ordinary moraines, will rarely be wanting. 



Those who have had opportunities of inspecting, in the sea off the 

 coast of Labrador, packs of icebergs which have run aground in 

 water having sometimes a depth of many hundred feet, describe 

 lagoon-like expanses of sea perfectly quiet, and free from all agitation 

 of the waves of the Atlantic. These areas of still water are sur- 

 rounded on all sides by icebergs from 100 to 300 feet high, frequently 

 containing moraine matter on their surface, or frozen into them. 

 Such icy masses may remain aground for weeks or months, until they 

 are reduced by melting to a size which admits of their floating off 

 and resuming their wanderings. The mud, sand, and boulders which 

 they let fall in still water must be exactly like the moraines of terres- 

 trial glaciers, devoid of stratification and organic remains. But occa- 

 sionally, on the outer side of such packs of stranded bergs, the waves 

 and currents may cause the detached earthy and stony materials to be 

 sorted according to size and weight before they reach the bottom, and 

 to acquire a stratified arrangement. 



I have already alluded (p. 146) to the large quantity of ice, con- 

 taining great blocks of stone, which are sometimes seen floating far 

 from land, in the southern or Antarctic seas. It is evident that such 

 glacial drift, wherever it may happen to alight on the floor of the 

 ocean, will have no connection with the external shape, or internal 

 composition, of the rocks on which it may chance to fall. After the 

 emergence, therefore, of such a submarine area, the superficial detritus 

 will have no necessary relation to the hills, valleys, and river-plains 

 over which it will be scattered. Many a water-shed may intervene 

 between the starting-point of each erratic or pebble and its final 

 resting-place, and the only means of discovering the country from 

 which it took its departure will consist in a careful comparison of its 

 mineral or fossil contents with those of the parent rocks. 



It will be seen in the next chapter that throughout large parts of 



