RAYMOND: CORRELATION OF THE ORDOVICIAX STRATA. ISl 



THE ORDOVICIAX 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, how^ever, 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 resume of the results of the work of Schmidt 

 and Lamansky. 



