386 GEOLOGY OF TOE DENVER BASIN. 



ciass i (^ = '-33). — This embraces the prairie coals of the lower Laramie. 

 They resemble in their physical appearance many bituminous coals of 

 the East, and in their fuel ratio certain coals in the lower portion of the 

 Pennsylvania bituminous series. Their proportionately great amount of 

 water, however, and the fact that the total percentage of fuel constituents 

 is much less than that universally present in the Eastern coals, prevent a 

 close relationship between the two series. The coal of Class I withstands 

 weathering well and is the highest of the coals about Denver in economic 

 value. 



ciass 11 (^ =I °7). — This embraces the coals of the foothills to a depth of 

 300 feet, At greater depths they approach Class I. 



ciass in (-;c=°-9 6 ). — This is el taracterizei 1 by the excess of volatile matter 

 over the fixed carbon, by the extremely large proportion of water con- 

 tained, and by the high percentage of ash. The coal of this class weathers 

 most readily upon exposure to the atmosphere, its color becoming brown, 

 its appearance earthy. It is a lignite, regarding- this term as signifying a 

 position above the peat and below a variety of coal commonly accepted as 

 near the base of the bituminous series in the East. It is a class in which 

 the fuel ratio oftener falls below than exceeds 1. 



SPECIAL SAMPLES OF COAL. 



The analyses of these coals are given in Table I. No. 37, from the 

 Garfield mine, represents a hard, smooth, pitchy coal, somewhat resembling 

 the higher bituminous and coking coals of the mountain regions. The 

 analysis shows it to be somewhat higher in fixed carbon and lower in 

 volatile-combustible matter than the general samples of the Erie-Canfield 

 Held. Its fuel ratio, L.55, places it considerably above the associated coals. 

 This variety is distributed without regularity through both the vertical and 

 the horizontal extent of the seams, but does not enter prominently into 

 their composition. 



No. 127, from the Simpson mine, is a typical specimen of conchoidal 

 coal. It is of frequent occurrence in the prairie coals of the bituminous 

 variety, forming prominent layers from 2 to 8 inches in thickness. It 

 resembles in its fixed carbon and volatile-combustible contents the run of 



