580 COAL MEASURES OF MARYLAND 



lifer, typical forms^ and Derhya crassa, associated with which are manv 

 other species. Amhocoelia planoconvexa is very abundant, its shells con- 

 stitnting a large part of the limestone at many localities. It is absent 

 or of rare occurrence in the Brush Creek limestone at most localities 

 east of Ohio. The Ames limestone is double at many places. 



The Portersville fauna is meager and not well characterized. It is 

 little known east of Ohio. 



The Cambridge fauna, though richer and much more widely extended 

 than the Portersville, is less profuse and apparently not so widely dis- 

 tributed as the Ames and Brush Creek faunas. It consists of marine 

 species in the western sections, but is more meager eastward, where it is 

 mingled with brackish water forms. In the Georges Creek basin it 

 appears to be replaced entirely by brackish water species. 



The Brush Creek fauna is characterized by the presence of many 

 Chonetes verneuilianus associated with other distinctive though less 

 abimdant species and by the absence of Amhoccelm planoconvexa ' and 

 the typical form of Chonetes granulijer at most localities east of Ohio. 

 The fauna is abundant, though less profuse on the whole than the Ames. 

 Like the Portersville and Cambridge, it is more meager eastward, fol- 

 lowing the apparent rule that more abundant faunas extend farther 

 east. 



The Brush Creek limestone, like the Ames, is found in a lower and 

 upper division in many places. 



Lithology. — The beds of this series may also be recognized by their 

 lithological sequence, systematically varying intervals, and the rela- 

 tions they sustain to the faunas over great areas. They comprise the fol- 

 lowins: members in descendino: order: 



Top. 



,. ^ , „ (Lpper division. 



Ames limestone and fauna .'^ .... 



) T>ower division. 



Harlem coal. 



Ewing limestone. 



Pittsburgh red sliale. 



Saltsburg sandstone. 



Porterville limestone and fauna (western sections) 



Coal. 



Cambridge red beds. 



Cambridge limestone and fauna. 



' AmliocixUa planoconvexa is cited by Condit from a numbei- of localities in the Brush 

 Creek of Ohio. It is. however, of rare occurrence at this horizon in the eastern sec- 

 tions. 



