90 STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 



the top of the section may represent the Lewis shale is very far 

 from improbable : there appears to be good reason for believing 

 that the Mesaverde of Rio Puerco includes the whole of the Pierre, 

 whereas at Cerillos, Mesaverde is Middle Pierre. 



Pierre deposits are exposed on the borders of the great San 

 Juan Basin. Information is lacking for the southern prong of this 

 basin but is fairly abundant for the main part, northward from 

 Lat. 35° 30', though comparatively few details have been published. 

 Gilbert,"- during the reconnaissance in 1873, measured a long sec- 

 tion of Cretaceous at Stinking Spring, 12 miles west from Fort 

 Wingate in New^ INIexico. This shows about 700 feet of yellow 

 shales, yellow sandstones with coal beds, resting on 1,050 feet of 

 sandstones and mostly sandy shales. Of the 7 coal seams, 3 reach 

 workable thickness ; one of them is triple, the benches being 4, 5 and 

 2 feet, separated by 5 feet and one foot of shale. There is no coal 

 in the basal 200 feet. The Cretaceous in this region is one litho- 

 logically ; " characterized by sands, by coal, by rapid alternations, 

 by ripplemarks and by oysters, it is evidently an off-shore deposit." 

 But fossils offer basis for subdivision ; they are abundant in the 

 lower 850 feet, which may be taken here as representing the shore 

 facies of Colorado or lower portion of the Mancos, as that appears 

 in the type locality. 



Thirty years later, Schrader"^ made a reconnaissance of .the 

 eastern side of the basin, from Gallup, near Fort Wingate, to the 

 northern border in Colorado. The section is longer than at Stinking 

 Spring and during the 30 years interval the coal bed had become 

 important. He found shales and sandstones, 2,000 to 3,000 feet 

 thick, with the Upper Coal Group in the lower part ; shales and 

 sandstones, 500 to 800 feet, with the Middle Coal Group near the 

 top; and 500 to 1,000 feet of Colorado shale, with the Lower Coal 

 Group near the top. The Upper Coal Group is about 100 feet thick 

 and contains 6 workable coal seams, 5 of which have fireclay floors. 

 The Middle Coal Group appears to be the same with that of Gil- 

 bert's section. The coal seams throughout appear to be irregular. 



G2 G. K. Gilbert, U. S. Geog. Explor. W. of looth Men, Vol. III., 1875, PP- 

 544. 549, 550. 



"3 F. C. Schrader, Bull. 285, 1906, pp. 242, 254, 255. 



