RAYMOND: CORREL.'^.TION OF THE ORDOVICIAN STRATA. 243 



see, eastern Missouri, and southern Illinois. The third and last 

 occurrence of Echinosphaerites is in a zone about 300 feet above the 

 strata containing the second occurrence, and in this highest zone 

 Christiania is abundant. This zone is found so far only at Strasburg, 

 Virginia, and near Chambersbiu-g, Pennsylvania. It is correlated 

 with the Trenton of New York. 



Pleurograptus linearis has been found in the typical Utica of this 

 country and here as in Europe marks a younger zone than that of 

 Dicranograptus clingani. Since, in Sweden, the beginning of the range 

 of Dicranograptus clingani is to be correlated with the last appearance 

 of Echinosphaerites, and, in Norway at least, the sedimentary record 

 from the Didymograptus geminus beds to the end of the Echinosphae- 

 rites beds seems complete, it would seem that we must parallel the 

 Echinosphaerites-Christiania beds of Europe with the Trenton and 

 Black River of America. The Middle and Lower Chazy would be 

 of the age of the Didymograptus geminus strata. Since the Jewe and 

 Kegel of Russia, seem to correspond to the zone of Dicranograptus 

 clingani and so to the Middle Trenton of America, and since there is 

 no radical change in fauna through the Jewe, Kegel, and Wesenberg 

 more than could be expected of various faunules in a single forma- 

 tion; and since further these formations contain some species found 

 in the Trenton of America, it seems that they most probably are to 

 be correlated with the American Middle and Upper Trenton, but 

 extending probably on into the equivalent of the Eden and perhaps 

 Maysville, though there is evidence of a very considerable break 

 between the Wesenberg and the Lyckholm, which is Richmond: 



Middle Ordovician. 



In Europe there is no distinct separation of the Lower Middle 

 Ordovician beds from those above, and I have used the above caption 

 merely to separate the discussion of the Didymograptus geminus and 

 Nemagraptus gracilis faunas from those which follow\ 



The most complete section is that in Norw^ay where the zone of the 

 first Echinosphaerites is followed by the zones of 4b, characterized 

 by Chasmops and Echinosphaerites. Zone 4ba, a shale with thin 

 layers of limestone, all very dark in color, is characterized especially 

 by Christiania and Chasmops conicopthalma. Here one finds also 

 species of Amp\'x, Lonchodomas, Remopleurides, Tretaspis, Sphaero- 



