586 GEOLOGY 



Hamilton fauna (Fig. 410). The northwestern fauna was so closely 

 allied to the Devonian fauna of eastern and central Europe that 

 free intercommunication between the two regions at the nortli is 

 inferred. The sea arm that reached down into the American in- 

 terior was perhaps no more than an eastern extension of the Eura- 

 sian Middle Devonian province. 1 The southward extension of this 

 great arm of the sea took place late in the Devonian period, for the 

 strata bearing its peculiar life lie on pre-Devonian formations in 

 Missouri, Iowa, and Minnesota, and overlie the Hamilton in the 

 more eastern region. 



Evidence of geographic connections. In Europe there is a 

 horizon so well marked by one species of brachiopod (Hypothyris 

 (Rhynchonella) cuboides) that it is known as the "cuboides zone." 1 

 This species also occurs in eastern Asia (China), in northwestern 

 America (Mackenzie valley), in western America (Great Basin), 

 and in the American interior as far east as New York (Tully lime- 

 stone). Several other species have a similar range. None of them 

 had close allies or progenitors in the Southern Hamilton. On the 

 other hand, allied forms have been found in England, Belgium, 

 France, Germany, Russia, Persia, and China. This seems to make 

 it clear that the derivation was from that quarter. A second wave 

 of European immigration is suggested by the fauna of the Portage 

 beds of western New York, characterized by an abundance of 

 goniatites. 3 A still later wave brought in some of the most char- 

 acteristic members of the Chemung fauna. The corals of the 

 Northwestern Hamilton fauna were of the Onondaga type, which 

 seems to indicate that at an earlier stage, the Onondaga fauna and 

 the ancestors of the Northwestern Hamilton fauna were in com- 

 munication, as might well have happened from the northern 

 habitat of both. 



The later Devonian (Chemung) fauna. The commingling mm 

 conflict which attended the invasion of the eastern and southern 



1 Weller, Jour. Geol., Vol. VI, p. 306. 



2 Williams, The Cuboides Zone and its Fauna, Bull. G. S. A., Vol. I, p. 

 481, 1890. 



3 Clarke, J. M., 16th Ann. Kept. N. Y. State Geol. and Mem. N. Y. State 

 Mus., Vol. VI. 



