334 PALEONTOLOGY. 



structures of coral." But recognizing, as Hunter did, the different 

 causes of geological phenomena, which later observers have established, 

 he returns to the aqueous ones, in all their modes, with the power of 

 solution, .... as the principal and most widely diffused power;" and most 

 beautifully and truly defines them as being, " although not the sole 

 formers, yet the regulators of the formation, of the surface of this 

 globe." 



The chief dynamical cause of change of the earth's surface which 

 has been determined, since the time of Hunter, in addition to those 

 which he recognized, is that of water in its frozen state. The disin- 

 tegrating power of water in passing from the fluid to the solid state, 

 though slow, is irresistible ; and is considerable in every latitude where 

 the temperature falls below the freezing-point ; the operation of masses 

 of ice or glaciers is more conspicuous and violent ; but its sphere is limited 

 in comparison with those of the great aqueous and igneous causes to 

 which Hunter refers. The appearances which glacial action has left 

 on many parts of the earth's surface were amongst the most remark- 

 able and problematical, until at length satisfactorily explained by the 

 observations, experiments, and calculations of some of the ablest geolo- 

 gists, profoundest mathematicians, and most enterprising voyagers at the 

 present day. 



The surface of the earth is affected by the movements of great 

 ice-masses or glaciers on land, and by the floating masses or icebergs at 

 sea. 



" The agency of glaciers," says Sir C. Lyell, " in producing permanent 

 geological change, consists partly in their power of transporting gravel, 

 sand, and huge stones to great distances, and partly in the smoothing, 

 polishing, and scoring of their rocky channels, and the boundary walls 

 of the valleys through which they pass." The stones carried along and 

 deposited by the glaciers are called the ' moraines.' There is always 

 one line of blocks on each side or edge of the icy stream, and often 

 in the middle, arranged in long ridges several yards high : the latter 

 medial moraines are due to the confluence of tributary glaciers. This 

 characteristic arrangement, or rather derangement, of parts of the 

 earth's surface by the movement of ice, with the scoring and polishing 

 marks of its transit, serves to indicate the former actions of glaciers in 

 localities where they have never been known in the memory of man, 

 and where the present cliinate is unsuited to their formation. 



In arctic and antarctic latitudes, vast masses of ice are annually de- 

 tached from the shores, and float off with more or less of the mineral 

 matter of such shores. Scoresby counted 500 of these bergs drifting 

 along in latitudes 69° and 70° N., which rose above the surface from 



