538 THEORIES EXPLAINING TRANSPORT OF BOWLDERS. 



of the materials being derived from the southern end of that delta, would have been 

 hurried along into the straits, strewing their bottom with a littoral deposit from the 

 Cumbrian mountains. This explanation, suggested as a possible case 1 , is attended with 

 insurmountable difficulties in the one under consideration \ for if we assume the delta 

 to be only 50 miles in length (not a third of the distance to which the bowlders have 

 been propelled), and that the slope of the delta did not exceed 3°, I am reminded by 

 my friend Mr. Lonsdale that its southern end must then have lain at the depth of 13,000 

 feet below the level of the sea. The hypothesis of the sloping delta from the shores of 

 Cumberland is, therefore, quite inadmissible. If this subject were fully entered upon, 

 many other difficulties, as the occasional immersion of the blocks in fine sand, &c, 

 might be suggested in inquiring how submarine currents of water can have impelled 

 onwards these gigantic bowlders. It might also be objected that this ebbing and flowing 

 of the tide is a complex question, barely within the limits of geological reasoning. If, 

 indeed, it be assumed that the district occupied by water was open at each end, as I 

 believe it was, then it is possible that the tides flowed in opposite directions ; as in the 

 Irish Channel, and to a much greater in the English. But I leave this abstruse point 

 in the hands of those versed in the laws of dynamics, hoping that at some future time 

 they may explain all the circumstances under which submarine currents may effect 

 the distant transport of large blocks, or whether such transport is impossible. 



A third theory refers the moving agent to ice, and originated, I believe, with Pro- 

 fessor Esmarck of Christiania, from witnessing the conveyance of stones by icebergs 

 during the thaw of glaciers, and their gradual advance upon adjoining plains. This 

 theory, being confined to subaerial phenomena, is of course inadmissible in our submarine 

 case. A new application of the same principle was suggested by M. Engelspach de 

 L'arriviere 2 , who from an observation near the mouth of the Niemen was led to believe, 

 that icefloes sailing out from rivers into seas, may, from the specific lightness of the ice, 

 have borne along many large blocks of stone and deposited them at great distances. 

 This opinion, being founded on the observation of a large block of granite so circum- 

 stanced, is well worthy of consideration, particularly since the theory has been much 

 improved by Mr. Lyell, who, combining this and other data, has shown that wherever 

 icebergs and icefloes have existed, this method of transport is unquestionably a vera 

 causa. The same reasoning may be applied to all those regions in which, from their 

 physical features, we may be sure that the cold is, or has been, sufficiently intense 3 . 



1 In a letter from the Rev. W. Whewell to myself, 1836, after my memoir on this subject was read before 

 the Geological Society. ' This ingenious letter contains much additional matter, which may, I hope, appear 

 hereafter in some work by Mr. Whewell, who having since been elected President of the Geological Society, 

 Willi trust show us to what extent physical science can be correctly applied towards explaining geological phe- 

 nomena. 



8 Considerations sur les Blocs Erratiques. Bruxelles, 1831. 



3 See Charpentier and Venetz on the Glaciers and "Moraines" of the Alps. Professor Agassiz has also 



