STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 89 



underlying Mancos. The lower portion of Mesaverde in Cerillos 

 is the great sandstone, 300 feet thick ; but in Hagan it is about 900 

 feet, mostly sandstone, without coal and with Pierre fossils at sev- 

 eral horizons. The coal group immediately overlying it is 180 feet 

 thick with 5 coal seams, of which one has local importance. This 

 averages about 3 feet in a small area and underlies a massive coarse 

 sandstone, cross-bedded and containing petrified wood. Thin 

 streaks of coal were seen in higher parts of the column. The whole 

 thickness is about 1,850 feet and the upper half has no marine fos- 

 sils. The Tijeras coal field, at 25 miles southwest, gives clearer 

 evidence of land conditions. The lower portion of the Mesaverde 

 is only 700 feet thick, but it contains 3 coal beds, 2 inches to 3 

 feet thick, proof that the broad sand flats were free from sea-inva- 

 sion long enough to permit accumulation of peat in the hollows of 

 their irregular surface. The lithology changes above the upper- 

 most marine sandstone. Exposures are such as to make measure- 

 ments indefinite, but the presence of what the writer takes to be the 

 Cerillos coal group is distinct, for two coal seams, 3 feet and i foot 

 6 inches, were seen. This upper portion contains no marine forms. 

 The basal deposit is a massive sandstone, 115 feet thick. 



The Rio Puerco field, beyond the Rio Grande, is about 25 miles 

 west from Hagan and Tijeras. Lee gives 1,700 feet as the thick- 

 ness of Mesaverde, but thinks that the upper part has been removed 

 by erosion. The Mancos (Colorado) shales are but 1,113 f^^t, 

 whereas they are 2,350 feet at Cerillos. The Mesaverde has many 

 horizons of marine fossils even to the top ; but, at about 300 feet 

 from the top as here exposed, it has a coal group, 185 feet, with 16 

 coal seams, all very thin ; and another, about 100 feet thick, with 

 one of the beds 6 feet thick, at 450 lower. Some of the sandstones 

 contain fossil leaves in abundance. At the base is a massive marine 

 sandstone, the Punta de la Mesa sandstone of Herrick and John- 

 son,®^ which is yy feet thick. The former existence of another coal- 

 bearing group is shown at the top of the column, where Lee found 

 at some localities a shale with thin coal. At the same time it seems 

 probable that the upper coal group represents that at Cerillos. Lee's 

 suggestion that the 300 feet of marine sandstone and sandy shale at 



61 C. L. Herrick and D. W. Johnson, Bull. Univ. New Mex., Vol. II., p. 6. 



