Il8 NEW YORK STATE MUSEUM 



made and unmade the Salina sea. The particular aspect of the 

 problem regarding the base of the Devonic that we are now con- 

 sidering has a somewhat localized significance in America, for the 

 lime sediments of this time, with their rich faunas, are quite es- 

 sentially (though not exclusively) of Appalachian origin. Through- 

 out the great stretch of the Appalachians from southwest to north- 

 east, the Helderberg seems only very gradually to become disen- 

 tangled from its Siluric affiliations. In the State of Maryland a 

 great mass of lime-clay sedimentation (Keyser member) lies at 

 the base of the Helderberg members as developed in New York. 

 There it embraces the maximum sedimentation of the lime seas 

 stage and its fossils have but partly disentangled themselves from 

 Siluric connections. In New York the place of this formation is 

 held by lime units which fail to carry the Helderberg fauna and are 

 therefore excluded from that formation. In Gaspe bay, on the 

 other hand, in the far northeast Appalachians of lower Quebec 

 (and probably in the extensively altered regions between New York 

 and there), the discordance between the Helderberg and the 

 Siluric is absolute, profound and fundamental. There the Siluric 

 failed entirely or has been ground out by overthrust. Farther 

 south in Gaspe, conformity is resumed in strata standing at extreme 

 angles, but here, at Perce and in the head of the Bay Chaleur at 

 Dalhousie, the aspect of the correlative lime sediments changes, and 

 in places a large element of Atlantic species is introduced into 

 the fauna and we are no longer dealing with like quantities. 



The sandstone transgression. It is well understood that the 

 shallow water transgression of the early Devonic was vast in its 

 amplitude. At no level in the Paleozoic column is the overriding 

 of the former shore lines by the shallow marine waters so emphatic- 

 ally marked. This extraordinary transgression resulting from a 

 slight but almost universal negative diastrophy, spread over the 

 earth a fauna of large proportions and homogeneous character, in 

 great part a derivative from the deeper lime sediments of the con- 

 temporaneous sea, but always an adjunct of the spreading shallow 

 waters. As the transgression proceeded, it carried with it species 

 out of their normal development basins into others where they never 

 became climacteric or elemental, but stand todaj as a key to the fact 

 and the direction of their migration. It has been thought that with 

 the close of the Siluric the great Arctic bay which reached down 

 into the interior of the continent had become largely obliterated, 

 but this contraction seems to have been essentially at the south and 

 the- northward and westward transgression Over the north Atlantic 



