202 



[Dec. 17, 



Mr. Lesley said, in presenting these notes, that he consid- 

 ered every field geologist entitled to the expression of his 

 opinions, but that only such as worked over the whole field, 

 and knew precisely all the facts in every part of it, would 

 be likely to see a clear way to the final resolution of its 

 difficulties. These difiiculties cannot be resolved on the 

 Ohio side of the coal field alone ; nor on the Alleghany 

 Mountain side of it alone ; nor by even an exhaustive obser- 

 vation in the north, nor by an exhaustive discussion of them 

 in the south. If there he " a northern rim " to the ancient 

 coal field, there must have been an eastern and a southern 

 and a western one also ; and no generalization will avail 

 that does not satisfy the data all around the compass — and 

 in fine, also, all over the interior area, where unfortunately 

 we have very few opportunities for study. 



These difiiculties are set forth in the preface to Mr. Piatt's 

 report H 5 on Armstrong county, in which the same sug- 

 gestion of an overlapping of the upper divisions of ISTo. XII 

 is made which Prof. White makes in these notes. But it 

 is there shown that the exhibition of No. XII along the 

 Alleghany mountain, and in Maryland and Virginia, as 

 well as in the northern counties, and. in the Anthracite coal 

 reo-ion of our own State, is not such as can be entirely 

 explained by the suggestion ; which has its value ; but 

 which must be cautiously followed as a guide in classifi- 

 cation. 



The combined labors of half a dozen geologists, all equally 

 competent as observers and theorizers — labors pursued unre- 

 mittingly now for half a dozen years — have not yet sufficed 

 to procure all the light we need to have thrown on the syn- 

 chronomy of even our own Pennsj^lvanian Carboniferous 

 and Devonian deposits ; and every fresh survey in a new 

 district like that of Mr. Jones in Maryland, and that of 

 Prof. Stevenson in Southwest Virginia, serves, among other 

 things, to throw doubt upon the shifting generalizations in 

 which too many otherwise judicious geologists are prone to 

 indulge — reversing the directions in which we look for the 



