DEVONIAN 329 



the Ithaca fanna. Associated with these Upper Devonian forms we find 

 several species characteristic of Middle Devonian horizons. Among these 

 are Pholidostrophia cf. iowensis, Cyrtina cf. hamiltonensis, SchucherteUa 

 chemungensis var. arctostriatus, Reticularia fimhriata, Nucleospira cf. 

 concinna, and species resembling the European forms Gypidula cf. 

 bipUcatus and G. cf. galeatus. Two possible explanations of this asso- 

 ciation of Middle and Upper Devonian species in the same fauna present 

 themselves. It has been shown by Williams and Kindle that Middle 

 Devonian species sometimes persist till late Devonian time and appear in 

 certain New York sections associated with Upper Devonian species.^^ It 

 appears most probable, however, from what we know of the relations of 

 Pugnax pugnus and its associated fauna to the Upper Devonian of New 

 York, that the occiirrence of Upper and Middle Devonian species in the 

 same fauna at Old Eampart is not the result of late persistence of the 

 earlier fauna. This species evidently migrated into the New York prov- 

 ince from the northwest in Upper Devonian time. The t^vo significant 

 facts of its association with Middle Devonian fossils in an Alaskan fauna 

 and its abrupt appearance in an Upper Devonian faima in the United 

 States, taken together, point very strongly to the probability that inter- 

 communication between the eastern Alaska province and the interior 

 American province M^as cut off during Middle Devonian, but became free 

 about the beginning of Upper Devonian time, when conditions became 

 favorable for the dispersal and migration of such forms as were adapted 

 to it. Some of the species which had during Middle Devonian time been 

 confined to this northern basin spread southward and helped to give a 

 distinctive character to the Upper Devonian fauna as we know it in the 

 United States. This appears to be the probable explanation of an associa- 

 tion of species which upon casual examination seems to afford contradic- 

 tory evidence as to the age of the fauna. If correct, the horizon 

 represented is Middle Devonian. 



DEVONIAN SHALE AND lONEOUS SERIES 



The Devonian limestone outcrops on both sides of the Salmontrout 

 river near its mouth. Brownish colored shales overlie the limestone here 

 and extend apparently to the top of the high ridge lying to the south of 

 the stream and represent a thickness of several hundred feet. No fossils 

 were found in these shales, but they are supposed to represent the Upper 

 Devonian. 



They are considered to be of Upper Devonian age, because tlieir relation 



" American Journal of Science, vol. 13, 1902, p. 429. 



