RAYMOND: CORRELATION OF THE ORDOVICIAN STRATA. 181 
THE ORDOVICIAN STRATA IN THE GOVERNMENTS OF 
PETROGRAD AND ESTHONIA, RUSSIA. 
% LOCATION. 
The Cambrian and Ordovician strata of western Russia outcrop in 
the northern parts of the Governments of Esthonia and Petrograd, 
| forming a narrow strip about 380 miles long, extending from the island 
[- of Dago along the southern shore of the Gulf of Finland to the eastern 
boundary of Esthonia at the Narowa River, thence eastward inland 
to the Sjass River, south of Lake Ladoga, and eighty-five miles east 
of Petrograd. This strip is roughly triangular, having at its widest 
portion in Esthonia, a breadth of thirty miles, and narrowing to a 
‘ point a short distance east of the Sjass. In Esthonia, west from Lake 
Peipus, the Ordovician is followed by the Silurian; while in the 
Government of Petrograd, the Devonian conceals the Silurian and 
overlaps successively lower and lower beds of the Ordovician, until 
east of the Sjass, it conceals all but a narrow band of Cambrian. 
This overlap of the Devonian on the Ordovician in the Government 
of Petrograd does not, however, indicate at all the absence of Silurian 
. in the southern part of that district, as many geologists have believed. 
Throughout the whole band, the older strata dip gently to the south, 
a dip which they apparently received in pre-Devonian times. Thus 
each successively higher stratum has its outcrop in an east-west band 
lying southward from its neighbor, and the Devonian, lying uncon- 
formably on these beds, conceals older and older ones according to 
the amount of its northward extent. (Plate 1). 
PREVIOUS WORK.’ 
As early as 1821 an Englishman, William Strangways, (52), pub- 
lished a detailed description and map of the strata in the vicinity of 
Petrograd, and since then various writers have described in great 
detail the Cambrian, Ordovician, and Silurian of this region. The 
principal writers on the Geology, as distinguished from the Palaeon- 
tology, have been Murchison, (35), Eichwald, (8), Schmidt, (42, 44, 45, 
47), Mickwitz, (33), and Lamansky, (29). Recently Bassler, (1), 
has published a short resumé of the results of the work of Schmidt 
and Lamansky. 
