SECTIONS OF ARZAMAS, THE PIANA, ETC. 
165 
Orenburg (R etepora jlustracea ?), the small spinose Producti and casts of Turri- 
tella. 
Whenever the sands which cover so large an area around Murom terminate, 
there the limestone shows itself, but as you approach Arzamas from the west, it 
is again hid hy a wide spread of black earth (Tchornozem). This handsome town, 
surrounded by the limestone, is built upon an elevated terrace, that decreases in 
height towards the river Tiosha, on the banks of which are yellowish white, con- 
cretionary limestones, covered by red clay and marl. The river runs for a long 
space through similar strata, and it is only on reaching Nova Salki on the road 
to Penza (fifteen versts from Arzamas), that the section is of real interest. Here 
the limestone becomes harder and more regularly stratified, with some finely lami- 
nated, compact beds, separated by thick bands of marl. These upper rocks, about 
forty feet thick, repose upon white gypsum, and are covered by red marls like 
those before alluded to near Kazan. 
Notwithstanding the concretionary character of the beds in one section, and 
their more regularly stratified appearance in another, it is quite evident, that all 
these masses belong to the same group ; similar fossils being disseminated at in- 
tervals. At Novo Salki they are rare, possibly on account of the large masses 
of gypsum which take the place of the limestone, but around Arzamas we found 
a spinose Productus absolutely identical with a species not uncommon at Hum- 
bleton Hill in the magnesian limestone of England (Sunderland) ; a Terebratula 
closely approaching to the T. Royssii with indeterminable forms of Spirifer, Area, 
Sanguinolaria, Modiola, Avicula , Corbula, Turritella and Pleurotomaria, and a 
Retepore scarcely distinguishable from R. Jlustracea. 
The river Piana, to the north-east of Arzamas, affords sections not less instruct- 
ive than those of the Tiosha. These localities, long ago described by Pallas and 
since adverted to by Mr. Strangway s 1 , are highly interesting. We followed the banks 
of the river for some distance by the villages of Itshalki, Kniaspavlova, andBarnix- 
kova, and ascertained that throughout this district it l’uns in Permian limestones. 
The hills on its banks have often very irregular surfaces, sometimes presenting 
great cavities due to subsidences, caused by numerous natural caverns of gypsum 
which forms the base of all the limestone of this tract. 
At Itshalki the limestone, near its upper limits, is so charged with fossils, 
that it has completely the aspect of a tertiary limestone, in which the shells are 
1 Geol. Trans., vol. i. p. 27. 
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