450 
The Hon. Mr. Strangways on the 
its being impeded by the fortuitous presence of the primitive boulders 
which have rolled into this principal valley or lowest trough of the 
district, and have been stopped by the more solid ledge of sand on 
which they have now settled. The same circumstance is of frequent 
occurrence in many of the smaller rivers round Petersburg, which 
consequently appear in many places like mountain torrents, whilst 
in others they are sluggish and muddy streams, perfectly suitable to 
the tame character of the country through which they flow. 
A sort of bar probably of a similar nature, exists opposite Schlusselburg; 
the Neva flows over it as it quits the Lake Ladoga. This forms a 
kind of lip or edge to the basin which contains the lake, behind 
which is deposited the greatest part of the earthy particles which 
the water may have collected ; hence the great purity of the waters 
of the Neva, and in general of all rivers at their exit from lakes. 
What the Neva deposits therefore lower down, must be chiefly if 
not entirely taken up in its own course, properly so called and not 
drawn off from the lake. The lake itself, at least the southern part 
of it, is so extremely shallow,* as to be scarcely navigable ; it 
probably rests upon the sand, without penetrating in any part to 
the clay. The limestone I have not traced myself thus far, but it 
is visible at Poutyelova, where I have examined it, and I have little 
doubt of its extending uninterruptedly along the hills which skirt 
the valley of the Neva on this side and of its joining the Tosna 
with Poutyelova, as I have found it to connect the Ishora with the 
Tosna. 
The great quarries of Poutyelova, which principally supply the 
capital with limestone for flags, are situated on the top of a high 
* The northern parts are very deep ; but there the coasts consist of harder and older 
rcseks and are much indented by deep bays. 
