coal. 383 



The percentage of volatile-combustible matter in the earlier samples of 

 coal from the foothill mines varies but little from the other early percentages 

 of the same column; it should, on the contrary, in view of the fixed carbon 



contents of these coals and a maintenance of the characteristics of the 

 prairie seams, have been much lower. The dynamic influences to which 

 the foothill coals have been subjected, resulting- in flexure and incipient 

 fracturing, would naturally be regarded as particularly favorable to the 

 escape of volatile matter, and a considerable relative decrease in the per- 

 centage of volatile hydrocarbons from that in the normal prairie coals would 

 have been expected. This would have accorded with experience in other 

 and similarly placed fields in various parts of the world. Instead, however, 

 of a decrease, a slight increase in volatile constituents is seen. In explana- 

 tion of this peculiarity it i.s suggested that after the lighter hydrocarbons 

 of the normal coal had been driven off by the increased pressure and heat 

 that accompanied the folding of the strata, facilitated by such crushing as 

 the beds underwent, their place was supplied by the partial breaking up of 

 the heavier hydrocarbons left behind, the amount of carbon thus becoming 

 diminished, while the volatile matter by increment remained the same. 



In the .Marshall group of mines the volatile-combustible matter shows 

 a variation from 32.60 per cent to 36.10 per cent, with an average of 33.D5 

 per cent. The workable area, however, is in close proximity to the general 

 fold along the base of the range, is considerably faulted, and altogether 

 presents greater opportunities fur variation in the volatile constituents of its 

 coal, by escape or otherwise, than the other regions of the Denver field. 



Among the analyses of samples from the Marshall held, Nos. 8 ami !l 

 afford an excellent illustration of the variation in the volatile-combustible 

 contents of coal from two different layers of what is, in the locality sampled, 

 a single seam, without parting. Of the two layers, one (No 9) is regarded as 

 an excellent steam coal, the other (No. 8) as more adapted to domestic uses. 

 The former, which constitutes the upper 2 feet <i inches of a 9-foot seam. 

 shows a fixed carbon content of 47.36 per cent with a volatile-combustible 

 content of 28.66; it is more fibrous and oily looking, and harder than the 

 bottom coal; in mining, it scales oti' in irregular fragments. The bottom 

 coal, on the other hand, has a fixed carbon content of 45.08, and its volatile- 



