CHAP. XVIII. TRANSrORTING POWER OF COAST-ICE. 363 



and jDosition before the drift and erratics accumulated on and 

 in them, and before the surface of the fixed rocks was polished 

 and furrowed. I have the less hesitation in ascribing the 

 transporting jiower to coast-ice, because I saw, in 1852, an 

 angular block of sandstone, eight feet in diameter, which had 

 been brought down several miles by ice, only three years before, 

 to the mouth of the Petitcodiac estuary, in Nova Scotia, 

 where it joins the Bay of Fundy j and I ascertained that on 

 the shores of the same bay, at the South Joggins, -in the year 

 1850, much larger blocks had been removed by coast-ice, 

 and, after they had floated half a mile, had been dropped in 

 salt water bj' the side of a pier built for loading vessels with 

 coal, so that it was necessary at low tide to blast these huge 

 ice-borne rocks with gunpowder, in order that the vessels 

 might be able to draw up alongside the pier. These recent 

 exemplifications of the vast carrying powers of ice occurred 

 in lat. 46° N. (corresponding to that of Bordeaux), in a bay 

 never invaded by icebet"gs. 



I may here remark that a sheet of ice of moderate thick- 

 ness, if it extend over a wide area, may suffice to buoy up 

 the largest erratics which fall upon it. The size of these will 

 depend, not on the intensity of the cold, but on the manner 

 in which the rock is jointed, and the consequent dimensions 

 of the blocks into which it splits, when falling from an 

 undermined cliff. 



When I first endeavored in the "Principles of Greology," in 

 1830,* to explain the causes, both of the warmer and colder 

 climates, which have at former periods prevailed on the 

 globe, I referred to successive variations in the height and 

 l^osition of the land, and its extent relatively to the sea in 

 polar and equatorial latitudes, — also to flu.ctuations in the 

 course of oceanic currents and other geographical conditions, 



* 1st edit. ch. viL ; Dili edit. ib. 



