100 THE DEVONIAN AND CARBONIFEROUS. [bull. 80. 



Iii this series no fossils appeared to help the correlations. The corre- 

 lation of Chemung Measures was based upon the appearance of Devo- 

 nian fossils, and in the strata where the fossiliferous beds were few and 

 the red rock similar to those above was prominent the designation 

 u Transition beds of Chemung into Catskill n is given. 1 



The report 2 on Potter County by the same authors, adds no new 

 features to the general problem of correlation — the report consisting of 

 detailed identification of the formations already classified and named. 



In the report 3 on Jefferson County the main part of the volume is 

 occupied with details of the township surveys. On pages xxvin to 

 xxxiv the author, Mr. W. G. Piatt, attempted a grouping of the forma- 

 tions that had previously gone under local names. The Lower Produc- 

 tive Coal Measures, aggregating about 300 feet in this county, he divided 

 into the Freeport group, the Kittanning group, and the Clarion group. 



The Pottsville Conglomerate No. XII, 300 feet thick, is subdivided 



into 



Homewood sandstones. 



Mercer group of coals and sandstones. 



Conoquenessing Upper sandstones. 



Quakertown coal. 



Conoquenessing Lower sandstones. 



Sharon coal and shales. 



Sharon conglomerate. 



H. M. Chance, 4 in 1881, compared the Millstone grit of Pennsylvania 

 with that of England. He said a survey of the Conglomerate No. XII 

 (Millstone grit) in Pennsylvania by Messrs. Chance, Carll, and White, 

 and of the same rock in Yorkshire, England, by Prof. Green and col- 

 leagues, led to the discovery of a striking similarity in the structure of 

 the rock in the two regions. 



A comparison of the nomenclature adopted by the two parties of 

 geologists is given, from the Sharon through the Conoquenessing sand- 

 stones to the Homewood sandstone of Pennsylvania, and the Kinder 

 Scout grit, coal, and Eough Rock of Yorkshire. Afterward, as the 

 middle members in both localities were sometimes represented by a 

 single rock and sometimes by several, a generalization was adopted 

 by each party, the second and third grits of the Yorkshire formation 

 being called the Middle grits, and the upper and lower Conoquenes- 

 sing sandstones of Pennsylvania, the Conoquenessing group. In the 

 modified nomenclature the Ohio or Sharon Conglomerate of Penn- 

 sylvania corresponds to the Kinder Scout or Lower grits of Yorkshire, 

 and the Rough Rock or Topmost grits of the latter to the Home- 

 wood sandstone of the former. 



• 



1 Geol. Survey of Pennsylvania, Kept, of Progress G', p. 50. 



2 Geol. Survey of Pennsylvania, Kept, of Progress, G 8 . The Geology 'of Potter County, by Andrew 

 Sherwood. Report on the Coal Fields, by Franklin Piatt. 



3 Geol. Survey of Pennsylvania, Kept, of Progress H 6 : Report of Progress in Jeflerson County, by 

 W. G. Piatt. 1880. 



4 Chance, H. Martyn: The Millstone grit in England and Pennsylvania; in Am. Jour. ScL, 3d aer., 

 vol. 21, 1881, pp. 134-135. 



