10 Mr Murchison on the Salt Steppe of Orenburg, 



we know of tlie plasticity of semisolids generally, especially 

 near their point of fusion. Many examples will occur to every 

 one of what they have observed of the plasticity of hard bo- 

 dies, — such as sealing-wax, for example, — exposed for a long 

 time to a temperature far below their melting heat, and which 

 have moulded themselves to the form of the surfaces on which 

 they rest. (5.) When the ice is very highly fissured, it yields 

 sensibly to the pressure of the hand, having a slight determi- 

 nate play, like some kinds of limestone, well known for this 

 quality of flexibility. (6.) I have formerly endeavoured to 

 shew how such a condition of semirigidity, combined with the 

 determined movements of the glacier, accounts for the re- 

 markable veined structure which pervades it. I am, my Dear 

 Sir, yours very truly, 



James D. Forbes. 

 Professor Jameson. 



On the Salt Steppe south of Orenburg, and on a remarkable 

 Freezing Cavern. By Roderick Impey Murchison, Esq. 

 Pres. G. S.* 



I. This salt steppe is distinguished from many of those which 

 are intei'posed between the Ouralsk and the Volga, or are si- 

 tuated on the Siberian side of the Ural Mountains, by con- 

 sisting not of an uniform flat resembling the bed of a dried up 

 sea, but of wide undulations and distantly separated low ridges ; 

 nevertheless it is, Mr Murchison states, a true steppe, being 

 devoid of trees and little irrigated by streams. The surface 

 consists of gypseous marls and sands, considered by the author 

 to be of the age of the Zechstein,t and it is pierced in the 

 neighbourhood of the imperial establishment of Illetzkaya 

 Zatchita by small pyramids of rock salt. These protruding 



* From the Proceedings of the Geological Society, vol. iii. part 2, p. 695 ; 

 having been read March 9. 1842. 



t His extensive surveys of Russia have convinced Mr Murchison, that 

 rock salt and salt springs occur in all the lower sedimentary rocks of that 

 empire, from great depths below the Devonian, or old red sandstone system 

 to the Zeclistein and the overlying marls and sandstones. 



