38-4 GEOLOGY OF THE DENVER 13ASIN. 



combustible matter amounts to .'36.18; it mines in blocks, and lias a con- 

 choidal fracture. 



The Scranton coal is remarkably low in its percentage of volatile- 

 combustible matter, the average lignite carrying about 40 per cent, 



The remaining coals of the Denver field vary but slightly in their 

 volatile hydrocarbons from the average for the areas in which they are 

 found. 



The water content of the coais. — The coals are readily comparable in regard to 

 this constituent upon reference to the older suite of analyses. In the 

 prairie coals of the lower Laramie the water amounts to 16.78 per cent, 

 in the foothill coals of the lower Laramie to 21.025 per cent, and in 

 the Scranton coal to 26.55 per cent. Of the coals of the lower Laramie 

 those of the prairie may be regarded as containing the normal water 

 content, since they are in the condition least disturbed and the nearest to 

 thai of original deposition. The foothill coals, on the other hand, are in a 

 vertical position, and in the flexing to which they have been subjected 

 have been considerably fractured; they have thus been brought into that 

 position which most readily permits the passage of water along bedding 

 planes and fractures opened up by folding, and are afforded opportunities 

 for the absorption of moisture not presented by coal in a less disturbed 

 region. The coal from the lower levels of the Old White Ash mine at 

 Golden shows, however, a distinct tendency, both in water content and in 

 other constituents, to revert to the normal prairie composition, these levels 

 being within a comparatively short distance of the curve to the gentle dip 

 which prevails beneath the prairies. The coal of the higher levels in all 

 the foothill mines, in fact, distinctly shows an increase in water over that in 

 coal from lower levels. This is not pit-water, but hygroscopic, which the 

 coal is enabled to absorb in greater degree as it is brought under the more 

 favoring conditions. 



The water content of the Scranton mines, the coal of which is upper 

 Laramie, is that of a typical lignite. 



A sh. — The ash of the Denver coals presents no peculiarities, unless in 

 those of the new < rolden mines, where it has risen to 7.70 per cent, the seams 

 being vertical or steep pitching, comparatively narrow, and divided by 



