Wm. F. Prouty — Meso-Silurian Deposits of Maryland. 565 



Silurian of Maryland was made in 1900 by C. C. O'Harra.* 

 He used the terms Clinton and Niagara, correlating the forma- 

 tions in Maryland with those in western New York. 



It has long been known by all geologists working in the 

 Appalachian districts that there is a marked stratigraphic 

 change as one passes westward over the protaxis of these moun- 

 tains. For the explanation of this fact the theory of a pro- 

 found fault was suggested by some but accepted by few. Sir 

 William Logan of the Canadian Survey, in 1866, suggested 

 the possible existence of a narrow basin of deposition west of 

 the protaxis to account for the stratigraphic break. 



It has also long been recognized that there exists a fau- 

 nal difference in some of the deposits west of the protaxis 

 in the Appalachians and in those west of the Allegany 

 Mountains in New York and the interior. The explanation 

 of this fact was little dwelt upon until recently, when E. O. 

 Ulrich and Charles Schuchert, after careful investigation 

 and faunal study, put forward a most admirably devel- 

 oped theory t to account for the apparent condition. They 

 conclude from paleontological evidence that there existed a 

 barrier of great length, which separated from the interior sea 

 a long and narrow body of water lying in the Appalachian 

 region, the " Cumberland basin," in which sediments were 

 deposited bearing fauna more closely related to the east Canada 

 and European deposits than to those of the interior sea ; that 

 the Atlantic crossed over the barrier forming the eastern side 

 of this basin in about Beekmantown time, but was restrained 

 by the western barrier of this basin from mingling with the 

 interior sea, possibly from Clinton but certainly from Niagara 

 time well into Oriskany time. The barrier forming the west- 

 ern side of the Cumberland Basin extended, according to 

 Ulrich and Schuchert, from the region of Cayuga Lake, N. Y., 

 southward to west of Altoona, Pa., thence parallel to the trend 

 of the Appalachian Mountains through central West Virginia 

 into eastern Tennessee. In discussing the fauna of the Cum- 

 berland Basin, Ulrich and Schuchert state that few species are 

 identical with those of the interior sea, and that the earlier 

 fauna recalls the Clinton, while it passes above into one which 

 may be compared to the Niagara. 



Charles Schuchert, in a later publication, ;); speaking of the 

 Maryland deposits which include the Clinton and Niagara, 

 says that save Atrypa reticularis and Lejptaena rhomboidalis 

 all the species appear to be new. Further, he directs attention 

 to the absence of such characteristic forms of the western or 



* The Geology of Allegany Co., Md. ; Md. Geol. Survey Kept., pp. 

 57-164, 1900. 



f Paleozoic Seas and Barriers in Eastern North America. N. Y. State 

 Mus. Bui. No. 52, 1902. 



\ Lower Devonic and Ontario Formations of Maryland, 1903. 



