12 Tke Amei'ican Geologist. juiy, i89i 
west slope of our mountaius. We cross the Sangre de Cristo 
range, the broad Sau Luis park and the Conejos range, seeing no 
coal for over 100 miles. From the Conejos range we look down 
on a region of endless plateaus, representing the La Plata coal 
fields. Over this large area there is, as we have stated, but half 
a dozen small mines. One bod}' of coal on the Animas river, be- 
low Durango, is seventy feet thick, caused b}- the running together 
of several seams. It is developed at the Carbonero and La Plata 
mines. The great bodv is traceable for several miles along the 
•' hog-backs'" !»}• a valley caused b}' the washing out of the softer 
coal. The individual seams composing this mammoth body can 
be worked individually to advantage, but worked collective!}' the 
result would be a high per cent, of ash from the admixture of 
shale "partings. " Close to the town of Durango a seam five feet 
thick, of excellent quality, is worked b}' the San Juan and Porter 
mines. The coal of all these seams makes ver}' good coke, but the 
market of it is at present local. The drawbacks to this coal field 
are its distance from the main central market, the presence of onl}' 
one line of railroad, and the proximity of the LUe reservation. 
When some of these obstacles are removed there is a good future 
for the region. 
An analysis of the smaller seams is : 
Percent. 
Water 0.63 
Volatile matter 34.70 
Fixed carbon .57.30 
Ash 7.37 
Total 100.00 
And for the larger seams : 
Per Cent. 
Water 1. 30 
Volatile matter 30.70 
Fixed carbon .54.78 
Ash 4.22 
Total 100.00 
Hills estimates the Colorado portion of this field 1,250 square 
miles, the available portion at 300 square miles, the available coal 
at 3,387,200,000 tons. 
FIELDS OF NORTHWESTERN COLORADO. 
From Ouraj^ we go northeast to Ci'ested Butte. Here is a small 
portion of the Grand River field isolated l)y a circle of volcanic 
mountains, forming the Elk ransje. The heat from these volcanic 
