46 The Middle Devonian Deposits of Maryland 



Marcelhis, Hamilton, and Genesee shales, according to the text, is repre- 

 sented as following down the valley of Wills Creek and entering Maryland 

 about where the western area of Eomney is mapped in the vicinity of 

 EUerslie. Along the state line on the Pennsylvania county map the lower 

 line of the Hamilton group is carried too far east of Wills Creek ; but the 

 general agreement is about as good as could be expected from the repre- 

 sentation on base maps of such great difference in topography. 



This agreement in the correlation of the formations in western Mary- 

 land and southern Pennsylvania is important for the Second Survey 

 virtually traced the Devonian and Silurian formations from New York 

 across the state to Maryland. The writer has studied a part of the 

 Pennsylvania region in the field and although in some of tlie classification 

 in the northeastern part of the state he differed from the Pennsylvania 

 Survey, in general the formations were accurately correlated with the 

 standard ones of New York. Furthermore, in reference to the claim 

 sometimes made that fossils are unreliable, it is to be said that in the 

 Pennsylvania Survey greater dependence was placed upon tlie lithology, 

 stratigraphy, and actual ti'acing of the formations in the field than upon 

 fossils. 



Since the Eomney formation in ^laryland is correlated so precisely 

 with the Onondaga, Marcellus, and Hamilton stages of New York, the 

 question naturally arises why the New York names are not fully accepted 

 for Maryland. As already stated there are obstacles in the way in attempt- 

 ing to map these divisions separately, due, largely, to the gradual change 

 from the lithological characters of one member to another so that in a 

 region of infrequent exposures it becomes difficult to represent a line of 

 division between them. It was deemed best to regard the stages as con- 

 stituting one formation. Tlie name Eomney formation was adopted which 

 had been proposed and defined for this division of the Devonian system 

 in the Virginias. 



Furthermore, the ^Maryland Geological Survey has used only those 

 names for its Middle Devonian and Upper Devonian formations which 

 are acceptable to the United States Geological Survey. 



