April 5, 1895.] 



SCIENCE. 



391 



SOCIETIES AND ACADEMIES. 

 NEW YORK ACADEMY OF SCIENCES. 



The Section of Geology and Mineralogj- 

 met !March IS, and after electing as officers 

 for the ensuing year, Prof. J. J. Stevenson, 

 chairman, and Prof. J. F. Kemp, secretary, 

 listened to a lecture by Prof. J. J. Steven- 

 son on ' The Origin of the Pennsylvania 

 Anthracite,' of which the following is an 

 abstract : 



Long ago H. D. Rogers showed that the 

 coal regions of Pennsj'lvania are divided 

 into longitudinal basins or troughs. The 

 first series embraces the area between the 

 Great Valley and the Alleghany Mountains 

 and contains the several anthracite fields 

 as well as the semi-bituminous fields of 

 Broad Top and the Potomac River. Bej"ond 

 the Alleghanies are six well marked basins 

 containing bituminous coal. 



Along a line from centi-al Ohio, eastward 

 to the Potomac coal field, one finds note- 

 worthy vai'iations in dip, the amount being 

 insignificant in Ohio, but very great in the 

 first series of basins. The increase is not 

 regular, there being no change practically 

 from the coke basins of eastern Pennsyl- 

 vania until within three or four miles of the 

 Potomac field, where the dip becomes very 

 abrupt. This line shows the extremes of 

 variations, for further northward there is 

 in all of the basins a diminution of disturb- 

 ance, even in the anthracite areas, while 

 southward there is a similar decrease, except 

 in the last. 



Analysis of coal samples from the Pitts- 

 bui^ bed, in the several basins, show a pro- 

 gressive decrease in proportion of volatile 

 matter toward the east or .southeast. H. D. 

 Rogers regarded this decrease as due to in- 

 fluence of steam or other gas escaping from 

 crevices madeduringthe folding ofthe rocks, 

 for he asserted that the volatile increased 

 aethe fiexures diminished in strength. Ste- 

 venson in 1877 showed that no such relation 

 exists. Lesley in lS7i> thought that earth- 



heat might have caused the change, as coals 

 in the anthracite region were buried under a 

 very deep covering of rocks ; but there is no 

 evidence that the coal measures were thicker 

 at the east than in western Pennsj'lvania, 

 while there is every reason for supposing 

 that the coal measures were thinner there 

 than at the southwest. There is therefore 

 no good ground for supposing that the earth- 

 heat would be efiective, for in Virginia, 

 where the thickness is very great, the coals 

 at the bottom of the column are verj' rich in 

 volatile matter. 



Professor Lesley has suggested that the 

 change in the coal might have been due to 

 oxidation. The rocks of the anthracite re- 

 gion are consolidated gi'avels with little of 

 argillaceous matters, whereas those of the 

 bituminous area are largely argillaceous, 

 which, being undisturbed, lute down the 

 coals, preventing percolation of water and 

 the escape of gases. But in fact the bi- 

 tuminous fields afford all types of coal from 

 highly bituminous to hard anthracite, and 

 sections in many portions of the anthracite 

 fields show more clay beds than do those in 

 S. W. Virginia where the coal is highly bi- 

 tuminous. 



It is not necessarj^ to regard metamor- 

 phism as the sole cause of anthracite. It 

 is not called in to explain a variation of 

 ten per cent, in the same beds within short 

 distances, and it cannot explain the occm-- 

 renee of bituminous in one bench and of 

 anthracite in another in the same opening 

 in Sullivan County, Pa., or equally of semi- 

 bituminous and dry anthracite in different 

 benches of the Mammoth. It does seem 

 as though the conversion of the coal must 

 have been practically complete before en- 

 tombment ; otherwise the variations of coal 

 of the same age in different areas would 

 seem to be inexplicable. 



In Pennsylvania the decrease in volatile 

 bears no relation to the extent of plication, 

 but it bears close relation to the thickening 



