

LIFE 413 



and Victoria and New Zealand, and the Lower Devonian especially 

 s considerable development in South America. 



Climate 



Conclusive evidence of great diversity of climate, or of variations 

 climate during the period, are not at hand. The Old Red Sand- 

 ne and the Catskill formation perhaps point to aridity, but this 

 hardly be affirmed. In formations thought to be Devonian, 

 f\i deuces of glaciation have been reported from South Africa, 1 

 but the evidence is perhaps not conclusive. 





th< 



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 th( 



int 



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LIFE 



The Marine Faunas 



At the beginning of the period shallow-water faunas were re- 

 stricted to limited bodies of water about the continental borders. 

 The life of these several bodies of water developed differently. The 

 early Devonian life consisted of the expansions of these provincial 

 faunas. When in the early Devonian the sea invaded the land from 



Jese different embayments, the advance from each carried its own 

 mewhat peculiar fauna toward the interior. The faunas invaded 

 the continent more or less simultaneously, but they reached the 

 interior more or less successively. The following faunas have been 

 :cognized: (i) the Helderberg, (2) the Oriskany, (3) the Onondaga 

 'Corniferous), (4) the Southern Hamilton, (5) the Northwestern 

 Hamilton fauna, and (6) the late Devonian fauna. They reached 

 the interior in the order named. As each in turn came in contact 

 with the preceding fauna, there was a mingling of the two, resulting 

 the destruction of some species and the modification of others. 

 A new, composite fauna developed from the survivors. 



Helderberg fauna. The Helderberg fauna seems to have 

 developed from the late Silurian fauna in the embayment at the 

 mouth of the St. Lawrence and on the border of the adjacent con- 

 tinental shelf, and perhaps also on the border of southern Europe. 

 It appears to have found its way into the Appalachian valley- 

 trough, and thence to have spread westward and northward, but not 

 beyond the eastern part of the great interior region. Perhaps it 

 reached the interior also from embayments on the southern coast. 

 The fauna had much in common with the contemporaneous fauna 



IHercynian) of southern Europe, but both differed markedly from 

 1 Schwarz, Jour. Geol., Vol. XIV, p. 683, and David, Q. J. G. S., Vol. XLI II. 



