409 
Geology of the Environs of Petersburg. 
baum ; is seen in the beds of most of the streams which discharge 
themselves into the gulf on this side, especially those between 
Becova and Peterhof ; appears farther inland through some of the 
boggy soils ; may be followed up the Ligovca to the lower lake of 
Doudorof ; up the Coirovca and its tributaries above the villages, 
where it is in great strength ; further eastward, it is to be found in 
the ditches along the Tzarscoe Celo road to the foot of Pulcova hill, 
on the Pulcovca above and below the remarkable outlier, and on all 
the streams cutting through that part of the escarpment. Again 
it is in great force on the lower part of the Ishora and Tosna 
rivers near Podolova and Nicolskoe. But further eastward, it 
seems the valley of the Neva and basin of the Ladoga, and with 
them the whole country, becomes too elevated to allow the 
denudations to lay bare this inferior bed.* The blue clay is said 
to be traced along the whole southern shore of the Gulf of Finland, 
at least as far as Reval. Above it lies an 
Intermediate Bed y 
which I confess myself to be unable to designate by any name 
derived either from its appearance or from its composition ; as it 
not only varies considerably in both, but consists of a number of 
alternating strata of various colours and substances, some of which 
are not always present, and where they are, differ greatly in their 
relative thickness and position. In fact, they appear to have no 
fixed relative position inter se , although taken as a whole, the 
series which constitutes that which I have named the intermediate 
bed is very constant in its place between the blue clay below and 
the limestone above it. It is also strictly intermediate in composition 
* The blue clay has been pierced to the depth of sixty-three feet, at the paper mill at 
Peterhof, and to twice or three times that depth on the banks of the Neva, without finding 
any Subjacent stratum. 
3 f 2 
