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Geology of the Environs of Petersburg . 403 
of which, for want of sufficient drainage, is now filled with peat bogs, 
while the edges or lips of these basins, which are, of course, much drier 
than the interior, become better adapted for agriculture, and are in 
consequence, together with the banks of the rivers, where the same 
cause operates, the only tracts inhabited and cultivated. To these 
may be added a few insulated deposits of gravel in some of the 
great bogs. But in every part of this country, over whatever stra- 
tum or in whatever situation, the superficial or vegetable soil is 
scanty in depth and poor in quality. A dry situation in a country 
generally so wet, and a climate, if not rainy, yet extremely variable, 
seems to be the principal object in the choice of a spot for building. 
Soil is but little considered in a system of agriculture where the 
peasant leaves his unmanured field fallow every alternate year, and 
where the government unavailingly offers rewards to procure from 
the land a return of five for one. 
ANTE-DILUVIAN FORMATIONS. 
Primitive. 
* Although no members of the primitive formation occur in situ 
within the limits of the tract which forms the subject of these obser- 
vations, yet it may not be unnecessary to mention the situation and 
* In the year 1819 , a Synoptic Table of the different formations near Petersburg, was 
published in French, in one sheet, in that city, by the author of this memoir, accompanied 
by a table of lithographic sketches and sections coloured ; also an oid duodecimo map of 
the Academy was issued anew, and coloured by the Mineralogical Society. 
From this table it appears, that with the exception of modern alluvium, and diluvian 
sand and gravel, the limestone No. I. is the most recent formation of that neighbourhood. 
From the nature of its animal and mineral contents it appears most nearly allied to 
the transition limestone of the English series. Beds connected with these deposites 
extend from Esthonia to the southern extremity of Lake Onega. 
