J. J. Stevenson — Use of the Name " Catskill." 331 



period and that its use as the name of an epoch be discarded ; 

 this, in view of the new light thrown upon the subject by his 

 paper. Mr. Darton has presented the conditions in the Cats- 

 kill Mountains with great clearness and he has increased our 

 stock of knowledge by the addition of details which till up 

 the gap for a portion of the southern border of New York, 

 but the writer cannot see that any light has been shed upon 

 the general problem of relations, which was not shining when 

 the Address, already referred to, was prepared two years ago. 



The making of names for local groups of rocks, if one 

 wish to employ them, is simple enough ; they may refer to 

 some physical character, to the distribution of some fossil or to 

 the locality itself. But to find a name for a vast formation is 

 far from simple. The problem is to give some definitive appel- 

 lation to a series of rocks covering or underlying many thou- 

 sands of square miles, showing variations in lithologic charac- 

 ters and in thickness, in the distribution or even in type of 

 animal or vegetable life. A name based wholly on paleonto- 

 logical grounds would be misleading ; equally so would be one 

 similarly based on lithologic characters. Evidently the only 

 recourse is a geographical term referring to some locality, 

 where one may find as nearly as may be, an average of all con- 

 ditions shown in the areas available for study. No name 

 should be given until after careful comparisons, that a wrong 

 typical locality be not selected. 



A single instance may be mentioned as illustrating the diffi- 

 culty. The term " Umbral," applied by H. D. Rogers to the 

 upper division of the Lower Carboniferous, being unaccepta- 

 ble, that group received from the 2d Geological Survey of 

 Pennsylvania the name of Mauch Chunk Red Shale. This 

 name answers well for the northeast corner of Pennsylvania, 

 in the vicinity of the anthracite region, but it is found less 

 and less applicable as one recedes from that region toward the 

 southwest and southwardly along the easterly outcrop line ; for 

 sandstones, limestones and shales of different types are found ; 

 soon the limestones become important ; eventually in the Vir- 

 ginias they predominate and the Mauch Chunk shales become 

 an insignificant feature of this group, which represents the 

 Chester and St. Louis, with part at least of the Keokuk of 

 the Mississippi valley. Long ago, W. B. Rogers gave to 

 this series the name of Greenbrier Group ; on Greenbrier 

 River of West Virginia the shales of northeastern Pennsyl- 

 vania and the limestones of southwestern Pennsylvania are 

 found developed to their greatest extent. This naming proves 

 to be defensible on paleontological grounds as well — in almost 

 every instance, careful stratigraphical and careful paleonto- 

 logical work come out closely in accord. 



