COAL OF THE DENVER BASIN, COLORADO. By GEORGE C. MARTIN. During the summer of 1908 the writer made a hasty reconnaissance examination of the coal field lying just east of the Front Range of the Rocky Mountains and extending from a point somewhat south of the city of Denver to the north line of the State. As the primary object of the work was the classification of the land, only sufficient time was devoted to the stratigraphy and structure of the rocks to enable the writer to compare his conclusions with those of the pre­ vious report 0 by the Geological Survey on this field. No important difference was found, and since the stratigraphic conditions to the north as far as the Wyoming state line are essentially the same as in the Denver region the statements of that report may be consid­ ered as applying to the whole field covered by the present paper. In general the sedimentary formations are steeply upturned against the mountains, but a few miles away the effect of the uplift disap­ pears and the strata are either horizontal or clip slightly toward the east at about the same rate as the slope of the plain. The structure is somewhat complicated near the mountain front by the sharp up­ turning of the rocks and by minor folds and small faults, which have caused considerable trouble in the mining of coal in this district. This condition, however, is local, and as the throw of the faults is small it has not proved to be a great detriment to the field. The principal coal beds occur in the lower part of the Laramie formation, which outcrops in a narrow band from a point west of Sedalia nearly to Marshall and there on account of faults and flatter dips expands into a wide belt of outcrop which extends northeastward from Marshall to Louisville and Erie, thence northward almost to the Wyoming state line, where it is covered and concealed by a wide over­ lap of Tertiary rocks. Active mining on these coal beds has been carried on for a long time, and in 1908 the combined coal production of Weld, Larimer, Jefferson, Adams, and Arapahoe counties, in which they are situated, oEmraons, S. F., Cross, Whitman, and Eldridge, G. H., Geology of the Denver Basin in Colorado: Mon. U. S. Geol. Survey, vol. 27,1896. 297 298 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1908, PART II. was 509,038 short tons. The coal meets with a ready sale, although it is inferior to much of the coal from other fields of Colorado, its nearness to a large city and to a region of intensive farming more than offsetting its poor quality. The coal generally is shiny and black and is inclined to be massive except as it separates along the planes of bedding. Joints are poorly developed and the coal breaks along irregular lines rather than in prisms like coal of a higher grade. On exposure to the air it rapidly parts with its moisture and in the consequent shrinking it breaks to pieces or air slacks. Its percentage of moisture is large, and conse­ quently shipment is expensive. Generally it is shipped in box cars to prevent the escape of moisture and the breaking down of the lump coal. During the present work a number of samples were taken from the mines of this basin for chemical analysis, and as the sampling and chemical work were done uniformly the results are particularly valu­ able in that they may be compared directly without the possibility of doing injustice to the product of any particular mine. The sampling, which is by far the most important part of the analytical work, was done by cutting a channel across the coal bed, including everything except the partings or lenses of foreign material which are present at many places. This cut included the entire bed or such part or parts thereof as are mined at that particular place. After being crushed in the mine to avoid loss of moisture and quartered in the usual way the final sample, weighing about 3 pounds, was sent to the chemical laboratory in sealed galvanized-iron cans. By this method the sample reached the laboratory in practically the same condition as it was in at the mine. As in this condition it may have included considerable moisture that in no way belonged to the coal, the sample was air dried in the laboratory to drive off all excess or easily separated moisture and then analyzed in the regular manner. Each analysis is given in four forms, so that it may be convenient for a variety of uses. The different forms are as follows: 1. As received: Analysis showing composition of the coal as it comes from the mine. 2. Air dried: Analysis of sample after it has been exposed to a temperature a little above that of the ordinary atmosphere and to a current of air. The sample in this condition probably is nearly the same as commercial coal, especially if the latter is shipped in box cars. 3. Dry coal: Analysis recalculated to represent the coal after all moisture has been removed. This form is valuable for purposes of comparison, but it should be clearly understood that it does not rep­ resent the coal as mined or as it reaches the consumer. COAL OF THE DENVER BASIN, COLORADO. 299 4. Pure coal: This heading is not strictly correct, for it implies that no foreign material is present, whereas the sulphur has not been eliminated. It is a convenient term, however, and is used in this report to represent coal in the hypothetical condition of having all its moisture and ash removed. Like, form No. 3, this is convenient for certain calculations, but in no way represents the coal actually mined and used. The chemical analyses of samples collected during the course of this work are as follows: Analyses of coal samples from the Denver Basin, Colorado. O [A. C. Fieldner, chemist in charge.] O Location. Thickness. Proximate. Ultimate. Heat value. o Labora­ Air- a tory drying Form of analysis. Volatile, Fixed Sul­ Hydro­ Nitro­ Oxy­ No. Sec. T. R. W. Coal bed. Part loss. Moisture. Ash. Carbon. Calories. B.t.u. g sampled. matter. carbon. phur. gen. gen. gen. 03 Ft. in. Ft. in. h-t 6371 24 4N. 65 2 8* 2 SJ 21.9 29.1 28.5 36.6 5. 82 0.30 6.55 48.95 1.03 37.35 4,667 8, 401 2 9.3 36.5 46.8 7. 45 .38 5.27 62.67 1.32 22.91 5,976 10, 757 *Z ' 40.2 51.6 8. 21 .42 4.67 69.07 1.45 16.18 6,585 11,853 K 43.8 56.2 .46 5.09 75.24 1.58 17.63 7,174 12,913 H 6372 33 3 S. 70 2 2 9.5 18.5 35.5 40.3 5.67 .57 5.76 53.15 .95 33.90 5,217 9, 391 ° 10.0 39.2 44.5 6.26 .63 5.19 58.73 1.05 28.14 5,765 10,377 B 43.5 49.5 6.96 .70 4.54 65.27 1.17 21.36 6,406 11,531 O 46.8 53.2 .76 4.88 70.15 1.26 22.95 6,885 12,393 0 6373 24 4N. 65 2 8 2 8 22.9 29.7 27.7 36.5 6. 10 .35 6.47 47.16 1.06 38.86 4,486 8,075 O 8.8 35.9 47.4 7. 91 .45 5.10 61.17 1.37 24.00 5,818 10, 472 g 39.3 52.0 8. 68 .50 4.51 67.07 1.51 17.73 6,379 11, 482 S 43.1 56.9 .55 4.94 73.45 1.65 19.41 6,986 12,575 O 6374 33 2N. 68 8 6 3 12.7 21.0 31.2 44.2 3. 61 .38 6.13 56.45 1.13 32.30 5,556 10, 001 £ 9.6 35.7 50.6 4. 14 .44 5.41 64.65 1.30 24.06 6,364 11,455 p^ 39.5 55.9 4. 57 .48 4.80 71.50 1.43 17.22 7,037 12,667 ' 2 41.4 58.6 .50 5.03 74.92 1.50 18.05 7,374 13, 273 o 6375 30 2N. 67 8 4 4 6 20.7 25.6 28.0 41.1 5.34 .36 6.27 51.81 1.11 35.11 5,101 9,182 2 6.2 35.3 51.8 6.74 .46 5.00 65.33 1.40 21.07 6,432 11,578 - 37.6 55.2 7.18 .48 4.60 -69. 65 1.49 16.60 0,857 12,343 ,_, 40.5 59.5 .52 4.96 75.04 1.61 17.87 7,388 13, 298 co O 6406 32 7N. 65 2 10J 2 10£ 26.1 31.4 28.1 35.1 5. 35 .46 6.68 45.57 .96 40.98 4,418 7, 952 ^° 7.2 38.1 47.5 7. 24 .62 5.12 61.66 1.30 24.06 5,979 10, 762 M 41.0 51.2 7. 80 .67 4.65 66.44 1.40 19.04 6,441 11,594 hi. 44.5 55.5 .73 5.04 72.06 1.52 20.65 6,986 12,575 £j 6407 29 3N.