58 Geological Society. Mr. Murchison's 



Pres. G.S., F.R.S., M. E. de Verneuil, Member of the Geological 

 Society of France, and Count Keyserling, was also commenced. 



April 20. — The reading of the Memoir on Russia commenced on 

 the 6th of April was resumed and concluded. 



With the exception of a sketch of the Ural Mountains, to be 

 given in a subsequent memoir, and of two short notices previously 

 read, on the Freezing Cave of Illetzkaya Zatchita, and on the 

 " Tchornoi Zem," or Black Earth*, the following abstract contains 

 the chief results of a second examination of Russia in Europe. 

 Following the same method as in the account of their first ex- 

 amination, the authors describe the depositary strata in ascending 

 order, successively adding to or correcting their previous know- 

 ledge of each mass of deposits. 



Silurian Rocks. — The boundaries of these the most ancient fossil- 

 iferous strata are more correctly defined than last year, and new 

 localities are cited. The lowest subdivisions of blue shale and un- 

 gulite grit, which were previously spoken of in certain inland spots 

 only, are now described in the sea-cliffs of the Baltic between 

 Reval and Narva, as well as on the banks of the rivers Narva and 

 Luga, in which situations, as in the tracts S. and S.E. of St. Peters- 

 burgh, they constitute the inferior masses or representatives of the 

 Lower Silurian Rocks. 



The Upper Silurian Rocks, chiefly composed of thin-bedded lime- 

 stone, occupy the summits of the coast-cliffs in question, and the 

 platform on which the river Narva flows from the lake Peicpus to a 

 chasm worn by its own action, where it constitutes the picturesque 

 falls above the Castle of Narva. It is believed by the authors that 

 this water-fall has receded (like those of Niagara, in America, and 

 other places,) in consequence of a solid tabular rock overlying less 

 coherent strata, which have been undermined and have occasioned 

 the subsidence of the superior layers. In addition, however, to 

 these conditions, the wearing away of the vertical cliffs of the Baltic 

 and the retrocession of the falls of the Narva, are supposed, by the 

 authors, to have been accelerated by another cause, viz. the direc- 

 tion of the symmetrical joints in the overlying limestone. These 

 joints present a number of salient and re-entering angles which are 

 exposed on the surface of the impending cliffs, and when the softer 

 supporting strata have been partially excavated, the dividing lines 

 of these natural joints facilitate the fall of the calcareous beds into 

 the abyss below. 



Besides the chief masses of limestone which extend over a con- 

 siderable tract in the province of Esthonia, (including the Isles of 

 Oesel and Dago,) the authors advert to a separate tract near the 

 small town of Schavli, in the government of Wilna, occupied by 

 upper Silurian rocks, which they discovered in their journey to St. 

 Petersburgh, and which they place as the highest member of the 

 system, or above the principal masses of the Orthoceratite and Tri- 

 lobite limestone and beneath the overlying old red or Devonian 



* See Proceedings of Geol. Soc. of London, vol. iii. pp. 712-714 ; [or 

 Phil. Mag. S. 3. vol. xxi. p. 357 j and vol. xxii. p. 71.— -Edit.] 



