iSS Mr Murchison on the Glacial Theoi-y, 



ing the facts with great perspicuity, he handles the whole subject witii 

 his usual master's hand, and points out the value of the previous obser- 

 vations of Von Buch, Brongniart, and other writers. M. Durocher con- 

 ceives that the phenomenon of the transport of erratic matters has pro- 

 ceeded from two successive and distinct operations : the first a great cur- 

 rent from the pole, to which the striae and polish of rocks, and the de- 

 posits called Osars, arc referred; the second, the transport of the distant 

 blocks by vessels of ice, when all that part of Europe which they covet 

 was subjected to the immersion of an icy sea. He does not agree with 

 M. Bohtlingk, that the point of departure of the current can be placed in 

 Lapland, but supposes it to have proceeded directly athwart those 

 regions from the pole *. But the point to which I now especially ad- 

 vert is, that in his skilful analysis of this memoir our eminent foreign as- 

 sociate admits floating ice as a vera causa to explain the drift of blocks, 

 just in the same manner as in common with Lyell, Darwin, and others, I 

 have been endeavouring to explain the phenomenon during the last three 

 years, and thus the inference which was drawn from plain facts is ad- 

 mitted, viz. that the chief tracts covered by erratic blocks were under the 

 9€a at the period of their dispersion. (Sil. Syst. p. 536.) 



Thus far had I written, Gentlemen, — in short I had, as I thought, ex- 

 hausted the glacial subject at all events for this year, — when two most 



* M. Durocher has made two valuable observations, in shewing us that the 

 striated and polished surface of the hard rocks is sometimes covered by accumu- 

 lations of sand and detritus ; and that althougli proceeding in a general sense 

 from the north, the furthest transported blocks are so distributed as to indicate 

 radiation from certain mineralogical centres, much in the same way as our blocks 

 of Shap granite have, on a less scale, been scattered from one point of distribu- 

 tion. In stating, however, that, in the progress of these transported masses to 

 the south, granitic blocks always constitute the outermost zone, it appears to me 

 that M. Durocher has generalized beyond the field of his own observation. In 

 Russia, for example, M. de Verneuil and myself traced greenstone blocks to the 

 same southerly latitudes as granites. The blocks between Jurievitz and Nijny 

 Novogorod are composed of quartz rock, and of the peculiar trappaean breccia 

 known in Russia as " Solomenskoi-kamen," the parent rocks of which we ex- 

 amined in situ near Petrazowodsk (Geol. Proceedings, vol. iii. p. 405), whilst the 

 extreme boundary of these boulders extends to Grarbatof on the Okka, S.W. of 

 Kijny Novogorod, and consequently very far beyond Kostroma, the limit assigned 

 to them by M. Durocher. Again, if M. Durocher prolongs the northern drift to 

 the flanks of the Ural Mountains, he is decidedly in error, for there is no coarse 

 detritus whatever on the flanks of that chain, whether derived from the north or 

 from itself. Of the Tchornoi-Zem, or black earth of the central regions of Rus- 

 sia, to which, quoting Baron A. de Meyendorf, M. de Beaumont refers in a long 

 note, I will now only say, that having studied the nature and extent of this singu- 

 lar deposit over very wide regions, I intend, with the help of my fellow-travel- 

 lers M. de Verneuil and Count Keyserling, to lay before the public very shortly 

 a sketch of its relations to the northern drift and other superficial deposits of 

 Europe. 



