8 BULLETIN 77, UNITED STATES NATIONAL MUSEUM. 



Table of Cambrian and Ordovician strata. 

 [Adapted after Kayser.] 





European Russia. 



North America. 



Upper Silurian 



Strata with smooth Pentamerus 



Oswegan (Clinton-Medina beds). 



Lower Silurian (Or- 

 dovician). 



Borkholm and Lyckholm beds 



Cincinnatlan. 

 Mohawkian. 







Trenton limestone. 



Black River-Birdseye limestone. 



Echinospherites limestone 





Va^inaten limpstorifi 



jchazy limestone. . . 



Beekmantown lime 

 stone. 



Quebec group 

 of Canada. 



Glauconite limestone 





Glauconite sand, Dictyograptus 

 shale. 



Upper Cambrian or 

 Olenus- (Dicello- 

 cephalus) beds. 



Ungulite sandstone 



Potsdam sandstone. 





Middle Cambrian or 

 Paradoxides beds. 





St. John or Acadian group. 





Lower Cambrian or 

 Olenellus beds. 



Fucoid sandstone, Blue clay, sand.. 



Georgia group. 



Von Schmidt's descriptions of the stratigraphy of the Russian 

 Cambrian and Ordovician are contained in several papers, chief of 

 which is his ''Revision des Ostbaltischen Silurischen Trilobiten."^ 

 In 1882 a short description of these strata by the same author ap- 

 peared in the Quarterly Journal of the Geological Society of London,^ 

 while still another article appeared in 1897, in the Guide of the Excur- 

 sions of the Seventh International Congress.^ From various sources, 

 but mainly from these several articles and from the collections in the 

 United States National Museum, I have compiled the following 

 notes on the stratigraphy of the region concerned in the present paper. 

 The stratigraphic relations of the rocks forming these notes are graph- 

 ically represented in the accompanying composite columnar section, 



CAMBRIAN STRATA. 



The sparing development of Cambrian rocks in the Russian Baltic 

 area is a striking feature. These rocks occur in a long, narrow belt 

 either paralleling or outcropping along the cliffs of the Gulf of Finland. 

 A lower blue clay and an upper sandstone deposit, usually not ex- 

 ceeding a combined thickness of about 100 feet, are the important 



iMem. de I'Acad. imp. sci. St. Petersburg, ser. 7, vol. 30, 1881, pp. 17-41. 



2 On the Silurian (and Cambrian) Strata of the Baltic Province of Russia, as compared with those of 

 Scandinavia and the British Isles. 

 » VII Congress Geol. Internat., 1897, pt. 12. 



