136 Murchison and Verneuil on the Geolof/ical Structure 



sea for a considerable time, the eastern boundary of that sea being probably 

 the slopes of the Ural Mountains. 



Drift and Erratic Blocks. — Overspreading all the formations, and greatly 

 obscuring them, is a vast mass of detritus, the large granitic and other 

 crystalline blocks of which have excited much attention, from the days 

 of Pallas to the present time. This detritus, the blocks of which have 

 all been derived from the north, is shewn to have been deposited under 

 the sea, or, in other words, upon a sea-bottom, since it covers the above- 

 mentioned shells. 



Notwithstanding the obscuration occasioned by this 'wide-spreading 

 drift, it is stated that the nature of the subsoil, or fundamental deposits, 

 can often be surmised from the colour of the superficial clay aud sand, 

 and the materials of small detritus, the surface of the Silurian zone being 

 gray, that of the old red, red ; whilst the cover of the carboniferous lime- 

 stone is often charged with many broken flints derived from the under- 

 lying beds of that formation, some of the siliceous fragments of which 

 have been transported farther southwards, and spread over the regions 

 occupied by the newer red and oolitic deposits. Thus, as all the larger 

 and harder blocks can be shewn to have been carried from the mountains 

 on the N.N. W., so in passing to the S.S.E. the finer ingredients, or ma- 

 trix of the detritus, is found to change by the successive additions of 

 materials derived from the denudation of the different members of the 

 palajozqic series. There is no instance of any substance having been 

 transported from S. to N., except by the modern action of streams, and 

 by local causes dependent on the present configuration of the land. Near 

 Nijnii Novogorod large blocks of a very peculiar trappean conglomerate 

 were detected, which had been derived from a rock in situ N. of Petra- 

 zowodsk, a distance of nearly 600 miles. In endeavouring to account 

 for the immense distances to which these blocks had been transported, the 

 authors expressed their belief that they had been floated in former ice- 

 bergs, which, breaking loose from ancient glaciers ivhich they suppose have 

 existed in Lapland and the adjacent tracts, were dislodged upon an eleva- 

 tion of the northern chain, and impelled southwards into the sea of that 

 period in which the post-pleiocene shells, to which allusion has been made, 

 were accumulated. In the relation of the blocks to the sea shells, they 

 conceive that Central Russia presents an exact parallel (though on a 

 much grander scale) to the phenonjena described by one of the authors 

 in the central counties of England, vfherc y similar collocation was ac- 

 counted for, by supposing that the northern l&locks were borne thither in 

 vessels of ice, which in melting dropped them upon what was then a sea- 

 bottom* 



Glacial Action. — After alluding to the works of Sefstrom and Bofclingk 

 upon the supposed '^ diluvial" currents of Scandinavia and Lapland, as 

 evidenced by the parallel strise and polishing of the Surface of the hard 

 rocks of these regions, the authors describe the most southerly of the 



* Silurian %5leni; p* 635^ tf»' ccq. 



