92 GEOLOGY. 



toma) and of cephalopods (Cardioceras, Perisphinctes, Olcostephanus , (Ecotraustes 

 Reineckia, Macrocephalites) together with other forms occur. 



At a higher horizon there appear significant species of Aucella of the types 

 represented by A. pallasi and A. brauni, associated with Avicula and Amusium i 

 and the ammonites Cardioceras (of the group C. alterinous), Perisphinctes, Olcos- 

 tephanus, and GEcotraustes, which belong to the northern fauna of Russia (the 

 "boreal" of Neumayr), while the coralline group named above appears to be, 

 allied to the more southern fauna of Europe. From the northern alliance it 

 is inferred that at some time in the closing stages of the Jurassic period, rather 

 free communication was established between the north Eurasian province and 

 the western shore tract of America, and that north Eurasian species migrated 

 down the American coast as far as Mexico, where Nikitin has identified the 

 " boreal" fauna in San Luis Potosi. As the great Jurassic transgression of the sea 

 was especially a northern movement, it is quite consistent that the northern 

 fauna should thus invade the western coast tract of America. The same fauna 

 spread south to the n rthern side of the Himalayan province, while the fauna 

 of the Cutch region on the Bay of Bengal still retained the central European 

 aspect, as did also that along the east coast of Africa (Mombassa) . 



The northern and more interior province.— The northern American province, 

 embracing parts of Dakota, Wyoming, and other states (Fig. 348) , with northerly 

 connections not yet worked out, bore a fauna of still more pronounced northern 

 affinities. A fine group Of ammonites flourished in Wyoming and the Black 

 Hills region {Cardioceras, Cadoceras, Quenstedioceras , and Neumayria), all of them 

 peculiar to the Callovian and Oxfordian horizons of the upper Jurassic (Hyatt. 1 ) 

 The species are not the same as those of the California district, which implies an 

 absence of free inter-communication. Belemnites were well represented (Fig. 

 369, c) and pelecypods (Ostrea stringileculia (Fig. 369, h), Camptonetes bellistriatus 

 (Fig. 369, d), Gryphcea calceola, Tancredia bulbosa, Pecten newberryi, Saxicava 

 jurassica, Mytilus whitei (Fig. 369, e), predominated. Curiously enough, no 

 gastropods have yet been found in this province. The ancient genus Lingula 

 (Fig. 369, j) had a diminutive representative, as did also the familiar Rhychonella 

 (Fig. 369, i). A crinoid and a starfish represented the echinodermsc 



It is noteworthy that Aucella, one of the most characteristic fossils of the 

 California province, has not yet been found in the Dakota province. It is found 

 in Alaska, in the Aleutian Islands, and in Russia. It was formerly supposed 

 that the Aucella migrated from Eurasia to America, because, as then known, 

 it ranged lower in Europe; but more recent investigations indicate that it 

 occurred quite as early in America as in Russia, and earlier than in England. 

 If the migrating tract between the Californian province and Asia lay along the 

 Pacific border, while the migrating tract between the Dakota province and Asia 

 lay in the Mackenzie basin and along the Arctic border, the two provinces only 

 coming into free communication far to the westward, it .is not difficult to under- 



1 Jura and Trias at Taylorville, California, Bull. Am. Geol. Soc. Am., Vol. Ill, 

 p. 410. 



