HYPOTHESES AS TO VARIATION IX VOLATILE. 51 



the considerable beds, while the latter is but 1,100 feet below the highest 

 stratum recognized in that portion of the Appalachian basin. Consider- 

 ing the whole of this 2,700 feet of rock upon the Sharon, that bed should 

 have a constant temperature of not far from 100° F. in Washington 

 county of Pennsylvania or about 30 degrees more than that of the 

 Washington coal-bed when it underlay the 1,100 feet. Comparing the 

 fuel ratios he finds in the two coals — Washington, 1.19 ; Sharon (block), 

 1.52 — a difference of 0.33 in favor of the lower bed, which may be due to 

 greater depth of cover or to difference in botany or to our having too few 

 analyses for obtaining trustworthy ratios or to other unknown or un- 

 suggested causes. 



He calls attention to the fact that our knowledge is incomplete respect- 

 ing the extent of the Coal Measures section ; that we know nothing re- 

 specting higher measures once existing in southwestern Pennsylvania, 

 but now eroded and sw^ept away. In the deeper anthracite basins the 

 Coal Measures, aVjove the Pottsville conglomerate, are 3,000 or more feet 

 thick ; and the type of the topography shows that still higher rocks must 

 have existed, though now they have been removed. He discusses the 

 distribution of the Permian beds, and considers that they must have in- 

 creased eastward, as do the other members of the series, so as to make 

 the top covering very thick in the anthracite fields and thinner in the 

 bituminous fields. In such case the coal-beds will appear to have been 

 subjected to more earth-heat in the« east and to less earth-heat in the 

 west, and their carbon ratios (so far as this cause is supposed to operate) 

 will be presumably higher in the east than in the west, as it undoubt- 

 edly is. 



A second suggestion arises out of the hypothesis that anthracite is due 

 to greater oxidation of the vegetable matter. Why should the beds of 

 the anthracite basins be more oxidized than those of the bituminous 

 fields? The rocks in the undisturbed western fields consist largely of 

 clay, while those of the eastern fields consist more largely of sand and 

 gravel strata, so that oxidation would be more favored in the latter. 

 More, the undisturbed clays of the west lute down and almost hermet- 

 ically seal the underground coals ; the disturbed, semi-metamorphosed 

 and cracked-up clay-slates of tlie east expose their coals throughout to 

 percolation, evaporation and oxidation. The regions differ in — 



1. Heavier covering of Permian at the east, raising earth-heat of the 

 anthracite beds. 



2. Greater constitutional looseness of whole pile of deposits in the east, 

 facilitating percolation and oxidation. 



3. Universal fracturing of the whole pile at the east, facilitating the 

 exit of the volatile hydrocarbon. 



