THE DEYOXIAX PERIOD. -151 



and northward as far as the advancing waters permitted. If the 

 interior waters did not extend southwesterly to the Heklerberg areas 

 of Tennessee, Illinois, and the Indian Territory, the aco - these 

 regions was probably gained through embayments from the more 

 southerly coast. The fauna seems never to have occupied the great 

 interior MissLssippian region generally. 



The Oriskany fauna, which followed the Helderbergian in tins 

 region, appears to have entered the interior region along the same 

 tracts as the Helderbergian. but to have spread farther westward, 

 even as far as western Ontario, while the Helderbergian fauna only 

 reached central New York. In its dominant phase, it was a sand- 

 loving fauna and crept along the arenaceous tract adjoining the old 

 Appalachian land and the northern shore of the interior sea. In 

 other areas where the deposit was calcareous, the fauna assumed a 

 modified ' phase. 1 The general identity of its lines of invasion with 

 those followed by the Helderbergian fauna, and the occurrence of 

 species of Oriskany aspect in the St. Lawrence embayment. offer some 

 suggestion as to its place of origin. A very significant fact also 

 is the occurrence of some very peculiar Oriskany-like species in 

 South America. This hints at the possibility that the fauna either 

 developed along the Atlantic coast in a horizon now entirely buried, 

 and certain of the species spread clown the coast and reached South 

 America, or else, originating at the south, certain species spread up 

 the coast until they found access to the interior through the inlets 

 mentioned. Some part of the fauna perhaps spread on to Europe 

 and to .Africa, or else was derived thence and spread westward, since 

 allied species occur in those regions. It is also quite possible that 

 some notable part of the fauna developed in the St. Lawrence embay- 

 ment at a stage later than the evolution of the Heklerberg fauna, 

 when the deposits became sandy, as they did. and that thence there 

 was migration more or less simultaneously southward along the coast 

 to South America, westward into the interior, and northward and 

 eastward to Europe and Africa. The more typical species of the 

 Oriskany. however, do not seem to have been directly derived from 

 Heklerberg species, but to haA'e been evolved in some distinct area. 

 The typical Oriskany fauna, on invading the regions already occupied 



1 Clarke. J. It. Mem. X. Y. State Iffus., Xo. 3. Vol 3. 



