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the far northwest, while further to the southeast the marine Llandeilian 
strata were deposited. Here we find the interesting Girvan deposits 
in which certain American faunal elements can be traced. 
Regarding the place of origin and the early centers of distribu- 
tion of gasteropods and cephalopods Dr. Ulrich has submitted 
the following observations : 
The oldest, in eveiywise unquestionable, fossil record of the coiled 
gasteropods and cephalopods is found in Ozarkian rocks. In fact these 
classes constitute the most important parts of the middle and later 
faunas of this period as developed in the Mississippi Valley. As but 
few species of these classes are found elsewhere in rocks of this age, it 
is assumed that the gasteropods and cephalopods originated in oceanic 
basins to the south of the Mississippi embayment, that is in the Gulf 
of Mexico, Caribbean Sea or South Atlantic. From there they spread 
to the north and west, attaining before the close of the Canadian 
period rather general distribution in the continental seas of North 
America. However, judging from the Baltic section, they seem not 
to have reached the European side of the Arctic until well into the 
Ordovician (post-Canadian). About the same time, or perhaps in the 
somewhat later Black River epoch, certain types of cephalopods, like 
Gonioceras, spread from the Arctic into the Pacific. (Revision of the 
Paleozoic Systems, Bull. Geol. Soc. America, 22, 1911, p. 503.) 
Regarding the crinoids, Dr. Ulrich states: 
The crinoids seem to have originated during the early Ordovician 
(post-Canadian) in the southern middle Atlantic, where the dominant 
types, as expressed in the invading Gulf faunas of this age are Dendro- 
crinidae, Hybocrinidae, and Rhodocrinidae. During the Silurian the 
Gotland crinoids, like the corals, spread freely through the Arctic and 
then southward in America to northern Illinois. They extended also 
southward into England, where a slightly different development 
obtained, and thence into the Atlantic to the Gulf of Mexico and the 
Mississippi embayment. All the succeeding Paleozoic crinoid faunas, 
so far as known, originated in and spread from the Atlantic basins. 
(Ibid., p. 502.) 
Regarding the time of origin of the crinoids it is interesting to 
note that, according to Dr. Holtedahl, fragments of silicified 
