Cm. VI.] 



OF AQUEOUS CAUSES CONTROVERTED. 



109 





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for tlie observed facts; but I shall endeavour to show, in 



that a combination of existing causes may 



the 



sequel,* 



In those regions the uneven 



have conveyed erratics into their present situations. 



The causes which will be referred to are, first, the carrying 

 power of ice, combined with that of running water ; and 

 second, the upward movement of the bed of the sea, convert- 

 ing it gradually into land. Without entering at present 

 into any details respecting these causes, I may mention that 

 the transportation of blocks by ice is now simultaneously in 

 progress, not only in the arctic and antarctic regions, but in a 

 part of the temperate latitudes, both of the northern and 

 southern hemisphere, as, for example, on the coasts of Canada 

 and Gulf of St. Lawrence, and also in Chili, Patagonia, and 

 the island of South Georgia, 

 bed of the ocean is becoming strewed over with ice-drifted 

 fragments, which have either stranded on shoals, or been 

 dropped in deep water by melting bergs. The entanglement 

 of boulders in drift ice will also be shown to occur annually 

 in North America, and these stones, when firmly frozen into 

 ice, wander year after year from Labrador to the St. 

 Lawrence, and reach points of the western hemisphere farther 

 south than any part of Great Britain. 



The general absence of erratics in the warmer parts of the 

 equatorial regions of Asia, Africa, and America, confirms the 

 same views. As to the polishing and grooving of hard rocks, 

 it has been ascertained that glaciers give rise to these effects 

 when pushing forward sand, pebbles, and rocky fragments, 

 and causing them to grate along the bottom. Nor can there 

 be any reasonable doubt that icebergs, when they run aground 

 on the floor of the ocean, must imprint similar marks upon it. 

 It is unnecessary, therefore, to refer to deluges, or great 

 oceanic waves, to explain the transportation of erratics to 

 great distances. 



As to variations in the tides in past times, they can never 

 have been sufficient to have imparted to marine currents, or 

 to the waves breaking on a coast, a degree of force greatly 

 exceeding that which they usually exert. When the excen- 

 tricity of the earth's orbit, of which more will be said in the 



* See also Elements of Geology, ch. 11, 12. 



