84 PROCEEDINGS OF THE ACADEMY OF [1892. 



1. The detached basins of the Rocky Mountain region, chiefly 

 of post carbouifei'ous date, which, though occurring over an exten- 

 sive territory, are mostly thin, small, widely separated, and often of 

 indifferent quality. 



2. The inaccessible and inconsiderable coal of the Arctic and 

 tropical regions. 



3. The relatively small beds of Nova Scotia and British 

 Columbia. 



After allowing such set off, and accepting the Census statement of 

 the remaining carboniferous area as equivalent to a veritable area 

 of mineable coal, we should have the latter fixed for the entire con- 

 tinent of North America at 219,080 square miles, which most 

 practical geologists will probably only consent to accept with grave 

 doubt, especially as no less authority than Professor Dana calcu- 

 lates the extent of the coal bearing area of the carboniferous measures 

 exposed in the United States at 190,000 square miles, of which only 

 120,000 have workable beds of coal; and for the whole of North 

 America at 208,000.^ It is not desired to intrude here too much 

 individual opinion, but after enjoying considerable opportunity of 

 personal observation of the great coal ; fields of the United States, 

 Nova Scotia and British Columbia, I do not myself believe that the 

 entire carboniferous exposures in North America contain 150,000 

 square miles of actual coal beds, including all qualities and thick- 

 nesses. Nevertheless it should be remarked in this connection, that 

 though no out-crops or other of the usual external indications have 

 been found, it is possible — though scarcely probable — that some of 

 the upper beds of the carboniferous series extending westerly from 

 the theatre of its greatest development, may underlie the rocks of 

 later horizon constituting the great western plains. But it is well 

 known that the lower members of the true coal measures thin out 

 and disappear in going west from Pennsylvania, until in the first 

 tier of States west of the Mississippi, only the highest beds in 

 general remain, and if these should continue to decline toward the 

 west in any such proportion as they do east of the great river, they 

 must entirely disappear long before reaching the territory occupied 

 by the cretaceous and later beds of the Rocky Mountain district. 



Of this assumed continental area of 219,080 square miles of coal 

 bearing territory, the available data for calculating the average 

 thickness with precision is as yet extremely imperfect. The rocks of 



*Manual of Geology, pp. 293. 



