472 A. W. GRABAU PALEOZOIC DELTA DEPOSITS OF NORTH AMERICA 



how Schuchert has his extensive calcareous deposits accumulating in 

 little shallow basins surrounded by land, each basin being in many cases 

 not much larger than one of our present Great Lakes. He must conceive 

 of North America as persisting in a chronic state of peneplanation, so 

 that only fine terrigenous sediments or none at all could be supplied. 

 Apparently little or no allowance is made for the subsequent removal of 

 the formations by erosion. 



Personally I am of the opinion that a large part of the calcareous 

 Niagaran strata extended over the interior and western portion of the 

 North American continent, and that extensive erosion during Middle 

 Siluric (Salman) time has removed a large part and subsequent erosion 

 a still larger part of these deposits. I believe that we will be forced to 

 come back to sounder stratigraphic principles than those now followed 

 by some American stratigraphers, and not regard every little deposit 

 faunally distinct from others as a separate invasion of the continent by 

 the sea. 



THE MID-SILURIC DELTA FANS OF NORTH AMERICA 



General discussion. — The Niagaran or Lower Siluric period of marine 

 deposition came to an end with the deposition of the Guelph-Lockport 

 dolomites of New York and Canada. Ulrich, to be sure, places the Louis- 

 ville coral limestones above the Guelph, but as this is evidently merely a 

 personal opinion of his, unsupported by evidence adduced, we may disre- 

 gard it. The Louisville is certainly the reef facies of the later Niagaran 

 deposits of the north, formed while the Lockport dolomites were accumu- 

 lating in the New York area and westward. This is where it is placed in 

 the much saner correlation table by Schuchert. 



Marine deposition was brought to an end by the general withdrawal of 

 the sea from the North American continent. This was probably largely 

 an epeirogenic movement, a general elevation of the land, accompanied 

 by local orogenic movements in the continent of Appalachia. Or we may 

 consider the withdrawal of the sea, this negative eustatic movement, as 

 due to deepening of the ocean basins, in which case we should expect to 

 find evidence of such withdrawal in other continents as well. There is 

 some indication to the effect that such withdrawal has taken place, fol- 

 lowed by a readvance of the sea. In Bohemia Barrande's Etage F 1; cor- 

 responding paleontologically to our Upper Monroe, rests with a discon- 

 formity on Etage E 2 . The latter appears to be Niagaran, though Car- 

 diola inter rupta suggests a somewhat later age. 



That the sea did withdraw from North America is clearly shown in the 

 sequence of the formation. Throughout the known areas of the conti- 



