Geology of the Environs of Petersburg . 
445 
to near the Gatchina road, and which is best examined near Verly, 
a smaller accident of the same nature is found lower down near 
Podolova, where the blue clay bursts from under the sand rocks. 
Of this I have given a small plan. The whole of this river is in- 
teresting, and the environs of Podolova and Cordelova even pictu- 
resque. Between Cordelova and Pilny Milny, I have not been able 
to inspect it myself. Fedorovsky is a high eminence of limestone, 
bounded by the sandy denudation of Pavlovsk, but offers nothing 
remarkable in itself. 
But by far the most romantic of all these streams is the Tosna, 
whose banks present at once landscapes to the painter, beautiful and 
rare flowers to the botanist, and perfect specimens of organic re- 
mains, together with interesting sections of strata to the geologist. 
From the large and flourishing crown village of Nicolskooy upwards, 
the banks attain a height of about two hundred feet, the lower 
part of which consists of naked cliffs, and the upper of hanging 
woods. At the village blue clay is seen in situ , and a little higher 
up, are cliffs of it 30 or 40 feet in height, perhaps the greatest 
strength in which it is shewm in any natural section. The top of 
one appears capped with red sand, under which, a few yards further 
on, the blue clay sinks to rise no more. The different strata of 
the intermediate bed now occupy the banks of the river for a space 
of three or four versts or more ; its subordinate beds are nearly the 
same as on the Ishora, but the entire mass is of much greater thick- 
ness. The bituminous clay beds are scarcely discernable. The red 
chamite bed is in great abundance, sometimes very hard. The 
larger chamites are found in a soft white or yellowish sand, which 
adheres to the lower part of some of the harder red strata, and 
when viewed from beneath some overhanging masses of rock, ap- 
pear like black spots, the nature of which would not readily be 
