566 Won. F. Prouty — Meso-Silurian Deposits of Maryland. 



Mississippian sea as Spirfer radiatus, Spirifer Niagarensis, 

 Spirifer Grispus, Spirifer sulcatus, Pentamerus oblongus, 

 Caryocrinus, and Fucalyptocrimts. Of these, Spirifer radi- 

 atus and Spirifer crispus are now known to occur in the Cum- 

 berland Basin. 

 I **X Mr. C. A. Hartna- 



gel of New York, in 

 ~~~ . an article* in 1902, 



; shows, however, that 



the western or Held- 

 erbergian barrier was 

 not continuously and 

 completely effective 

 from Clinton to Oris- 

 kany time, since the 

 mingling of Guelph 

 and Cobleskill fauna 

 evidence the crossing 

 of the barrier during 

 Cobleskill time. 



Up to the present 

 less than half a dozen 

 species of fossils have 

 been definitely de- 

 scribed from the Mary- 

 land, Clinton, and 

 later Meso-Silurian. 



General Descrip- 

 tion. — The outcrop of 

 the Meso-Silurian 

 rock in Maryland is 

 limited entirely to the 

 region of the Alle- 

 ghany Ridges proper, 

 in Washington and 

 Allegany Counties. 

 The area covered is 

 about twenty - four 

 square miles, of which 

 the Clinton occupies 

 fifteen and the Later 

 Meso - Silurian about 

 nine. As would be expected from the general Appalachian 

 structure, the rocks under discussion flank anticlinal folds which 



* Preliminary Observations on the Cobleskill Limestone of New York. 

 Eept. N. Y. State Paleont. for 1902, p. 1156. 



