580 Geological Society '. Anniversary AddresSfl^^^. 



Russia, must have taken place (as I believe at least) when those flat 

 regions were beneath the sea, for recent observations have shown, 

 that the blocks constitute the uppermost or last surface deposit in 

 tracts which exhibit, here and there, proofs of having been an ancient 

 bottom of a sea. But without extending his theory to other parts 

 of the world, it does not appear to me, even wlien confined to the 

 Alps, that INI. Necker explains satisfactorily how the granite blocks 

 of Mont Blanc should lie upon the Jura, by any reference to sub- 

 aerial debacle ; for if we are to imagine the deep hollow of the lake 

 of Geneva, filled up with gi-avel, sand and mud, and forming an in- 

 clined talus from the centre to the flanks of the chain, the subse- 

 quent scooping out of this enoi'mous mass of materials involves an 

 intensity of degradation as diflicult to beheve in as the former extreme 

 climate of Agassiz, by which thousands of feet of snow and ice are 

 supposed to have occupied the same deep valley. I ought not to 

 omit to state that one of the chief elements introduced by Agassiz 

 into this question, the polished and striated surfaces of the rocks, 

 has not yet been alluded to by this author, but will be treated of in 

 his second volume. 



In the mean time, however he may fail to account satisfactorily 

 for the transport of the very distant great blocks, we have to thank 

 M. Necker for the additional materials, which seem to establish one 

 fundamental fact in reference to the Alpine case, viz. when this 

 detritus was cast off', the gorges and flanks of the chain had nearly 

 the same reference to the central crest as that which now prevails. 

 If this be proved, the theory Avhich depends chiefly upon the sup- 

 position, that a great elevation of the centre of the chain broke 

 off" the ice and dislodged the glaciers, is deprived of its chief basis. 

 In what manner Professor Agassiz can account for the Alps being 

 a great centre of dispersion wJien at a lower level, is indeed a part 

 of his theory which is not easily comprehended. On the other hand, 

 whatever we may think of M. Necker's hypothesis, it must be ad- 

 mitted that the facts adduced by him support one essential point of 

 the glacialists, by connecting the presence of blocks with the exist- 

 ence of glaciers in the Alps, the former being, as he states, inva- 

 riably found both in the southern and northern watersheds of those 

 mountains, and at the mouths of the great transverse ravines which 

 lead up to the regions of jierpetual snow, and in all such cases he 

 allows that the condition of the blocks is highly indicative of their 

 having once formed part of the " moraines " produced by former 

 glaciers. 



But the important point, that the glacier is the chief source of 

 the origin of erratic blocks, is entirely denied by another antagonist 

 to the theory of Agassiz, who has appeared in the person of M. 

 Godeftroy *. 



After the observations of two summers in the Alps, this author 

 has become convinced that the materials of the so-called moraines 

 have not been derived simply by the glacier from the solid rock in 

 the higher mountains, but arc the re-arranged portions only of a 



* Notice sur les Glaciers, les Moraines ct les Blocs Erratiques, 1840. 



