STEVENSON— IXTERRELATIOXS OF FOSSIL FUELS. <)3 



Colorado on both sides of the Front Ranges. Near Durango, three 

 workable coal seams are present within a vertical distance of no 

 feet, midway in the iMesaverde ; these become insignificant toward 

 the east and no workable seam was seen along the outcrop for more 

 than 60 miles. But at Monero in New Mexico, three seams of 

 workable thickness are present in a vertical distance of 100 feet 

 above the basal sandstone. 



The Uinta Basin extends from the westerly foot of the Wasatch 

 Mountains in Utah into northwestern Colorado and has an area of 

 not far from 10,000 square miles, being a little larger than the San 

 Juan Basin. The Utah prong, known as Castle Valley, was ex- 

 amined by Taff and by Lupton, while Gilbert has given the section 

 in the Henry ^Mountains about 50 miles southeast.*'^ The highest 

 Cretaceous beds in the Henry Mountains are the ]^Iasuk sandstone 

 and Masuk shale of Gilbert, the former containing coal seams ; it is 

 thought by Lupton to be most probably Mesaverde. Lupton made 

 no detailed study of the Mesaverde in Castle V^alley, but estimated 

 the thickness as not far from 1,200 feet and notes that it contains 

 several important coal beds in a section of 500 feet, beginning at 

 200 to 300 feet from the base. Taff notes the triple structure of the 

 Mesaverde, the two sandstones separated by the coal group. The 

 coals are numerous but are important only in the lower 250 feet of 

 the group. The coal is massive, bright, clean, bituminous and con- 

 tains much resin. Partings are usually insignificant, but Taff saw 

 one in a thick coal seam, which increased from nothing to 16 feet 

 within 2,000 feet. The roof and floor of the coal seams are often 

 sandstone. 



Richardson examined the southern side of the basin between 

 Sunnyside, L^tah, and Grand River, Colorado, known as the Book 

 CliiTs coal field. '"^ The thickness of the INIesaverde is given as 1,200 

 to 2,200 feet, the variation being due to erosion. The underlying 

 Mancos shale contains Pierre fossils in the upper 250 feet and is 

 nonfossiliferous for a great thickness below ; so that the ]^Iesaverde 

 is not lower than Middle Pierre. The sandstones of the formation 



^^ G. K. Gilbert, " Geology of the Henry Mountains," U. S. Geog. and 

 Geol. Survey of the Rocky Mountain Region, 1877, pp. 4-10; J. A. Taff, Bull. 

 285, 1906, pp. 292-294, 298; C. T. Lupton, Bull. 628, 1916, p. 34. 



"° G. B. Richardson, Bull. 371, 1909, pp. 7-39. 



