PALEOZOIC FORMATIONS OF MARYLAND 413 



called the Rockwood formation in the Piedmont folio of the U. 

 S. Geological Survey. 



Niagara formatio7i. — This formation surrounds the three areas 

 mentioned under the Clinton formation. The lower part con- 

 sists of thin-bedded, blue limestones with thin shale partings; 

 but in the upper part the shales predominate and become black- 

 ish in color. The thickness varies from less than 250 to fully 

 300 feet. The thin limestones contain brachiopods and other 

 fossils, some of which are specifically identical with the Niagara 

 fossils. The formation is named from the admirable exposures 

 at Niagara Falls and represents No. \b of the Pennsylvania sur- 

 vey and the lower part of the Lewistown formation of the Pied- 

 mont folio. The revised classification of the New York series by 

 Messrs. Clarke and Schuchert, however, drops the Niagara 

 formation or group and returns to the earlier classification 

 of Rochester shale, Lockport limestone, and Guelph dolo- 

 mite.^ 



There has been more or less uncertainty regarding the iden- 

 tification of the Niagara limestone south of New York ; but 

 recently Dr. Weller has conclusively shown that the Decker 

 Ferry formation of western New Jersey and eastern Pennsyl- 

 vania is of the same age "as the Rochester shale and Lockport 

 limestone of Clarke and Schuchert, or as the Niagara formation 

 of most authors."^ A small collection of fossils from the beds 

 near Cumberland was submitted to Dr. Weller who kindly exam- 

 ined them and wrote that his impression is that they are the 

 same as the Decker Ferry formation, and in New Jersey there 

 are sufificient authentic Niagaran species to definitely refer the 

 formation to the Niagaran. In conclusion he stated that " I 

 should think you would be fully justified in considering the 

 Cumberland fauna as of Niagaran age." 3 Mr. Schuchert has 

 studied these beds in the field as well as their fossils and he posi- 

 tively correlates them with the Niagara. His statement is that 



' Science, N. S., Vol. X, 1899, p. 876. 



^Geol. Surv. N. J., Ann. Rept. for 1899-1900, p. 18, and also see p. 20. 



3 Letter of May 29, 1901. 



