28 The Hon. Mr. Strangways on the Geology of Russia. 



selenite *. The neighbouring country is all red rock marl^ in which the ala- 

 baster forms subordinate beds. 



About eleven versts higher up the river Piana, is the village of Tzaitska, 

 situated on the side of the ridge of hills that extends from Barnoucova. An 

 ancient wooden church in the most grotesque style of Russian architecture 

 .stands on a bank^ the structure of which is laid open in a cliff just below it. 

 Regular horizontal strata of red marl are discovered alternating with grey and 

 white beds, of the same nature as at Nishney Novgorod ; and as at that place, 

 the grey beds contain a substance which has been taken for the mineral called 

 rock-leatherf, but which on examination proves to be a coriaceous form of 

 fibrous gypsum. It is interposed in continuous layers between the beds of 

 marl, and might be pulled out with care in sheets of several square feet, as it is 

 very tough. I have not found it anywhere in so perfect a state as at Troitska, 

 though it occurs more or less in all the marls of this district. The only diffe- 

 rence between the appearance of the cliff at Troitska and those at Nishney, 

 is, that in the latter instance small beds of sandstone occur, which are wanting 

 in the former. The vegetable soil which covers the cliffs on the Oca, is of a 

 deep red, like the rock itself; while at Troitska it is a thick bed of jet black 

 mould, although the rock below is exactly similar in colour and nature to that 

 of Nishney. 



The red marl continues to be seen along the banks of the Volga, and pre- 

 vails in the governments of Cazan and Simbirsk: the most distant locality of it, 

 that I can mention with certainty, is at Tetushy, which is built on the summit 



* Where the beds of alabaster pass into the red marl, they form a pale-coloured compact lime, 

 stone, containing selenite. This would naturally be the bed in which to look for gypseous shells 

 like those of Novinski, but I was not lucky enough to discover any decided trace of organic re- 

 mains. 



+ See Mem. de I'Universite de Moscou, p. 253. — The mineral which Dr. Pansner is there 

 said to have brought from Nishney Novgorod, is identical with that of Troitska here described, 

 and is found in similar beds in situ in the red marl. It is quite evident that this cannot be an 

 alluvial product, or have come out of a hill of alluvium (400 feet in height). That which is 

 described by Professor Fischer, in a subsequent part of the same paper, as found near Mourom, 

 is identical with what will be described hereafter under the head of Vixa ; except that instead 

 of occurring in ironstone, it is in a calcareous concretion like what I have found at Myavetz 

 Pavolskoy ; this concretion may have been in alluvial soil. 



Having seen the specimens in both cases, in the possession of those who found them, and hav- 

 ing visited the localities and found the minerals myself in situ^ there and in other parts of the 

 same district, I am enabled to speak positively upon this subject. 



Coriaceous gypsum occurs also in the red marl of Devonshire. 



