226 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
Chiron limestone of Kinnekulle and Oeland, serves to indicate that 
the upper part of the Orthoceras limestone in these localities is the 
equivalent of the Nemagraptus gracilis shale as well as the Geminus 
shale. And the correlation of the Chasmops limestone with the grapto- 
lite shales of the Dicranograptus clingani and Pleurograptus linearis 
zones is assured by the presence of several species common to the two 
types of deposits. 
CORRELATION OF THE AMERICAN WITH THE 
EUROPEAN FORMATIONS. 
In attempting a correlation over such a distance one is of course 
obliged to depend very largely on fossils; and it is necessary to assume 
an hypothesis which all the evidence seems to support, namely, that 
cosmopolitan faunas reach their wide distribution within a very short 
- space of time. In the present case, it is necessary to depend very 
largely upon the graptolites which seem to be more widespread than 
any of the other organisms. Graptolites are, of course, almost absent 
from Russia, so that it is necessary to correlate the Russian with the 
Swedish sections by means of other fossils. The trilobites, being best 
known, have been used most, but in certain cases species of brachio- 
pods, cystids, or cephalopods have proved of prime value. 
After making many groupings of the formations and testing many 
tentative correlations, it has seemed that the most logical arrange- 
ment is secured if the principal weight is given to the graptolites. It 
appears that these organisms had spread very much more rapidly than 
any of the other animals, except for a few thin-shelled brachiopods and 
‘trilobites which may have been dispersed by the same agency as the 
graptolites. When relatively short distances are in question, it seems 
that the bottom dwelling animals were able to keep pace in their 
migrations with the graptolites, at least sufficiently closely so that we 
detect no difference in the geological record, but when long distances 
are traversed, the bottom animals lag very considerably behind. 
Striking cases are those of Shumardia, which preceded the first Tetra- 
graptus fauna in Scandinavia, and reached America only with the last 
Tetragraptus and the first Diplograptus, and of Echinosphaerites, 
which preceded the Nemagraptus gracilis fauna in Scandinavia and 
followed it in America. 
