STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 



83 



as somewhat older. At the same time, in view of conditions farther 

 north along the eastern foot of the Front Ranges, the writer feels 

 compelled to abide by his opinion expressed 35 years ago, that in 

 large part, at least, the rocks belong to the Fox Hills. The basal 

 sandstone known now as the Trinidad sandstone (Halymenites sand- 

 stone of Stevenson), contains some marine fossils with great abun- 

 dance of the fucoid, Halymenites major; the overlying beds, wdth 

 extreme thickness of about 500 feet, are prevailingly sandstone with 

 interbedded shales and coal seams. The rocks have fossil leaves, 

 which are older than Laramie and a few marine fossils have been 

 seen. The coal seams are numerous but are indefinite, varying so 

 greatly in thickness and relative position that correlation, especially 

 of the higher ones, is not possible. All are excessively variable in 

 the New Mexico portion of the field, but some of them attain im- 

 portance in modest areas and are mined extensively. In the 

 northern or Colorado part of the field there are from one to 8 seams 

 in the 250 feet above the Trinidad sandstone. This group is per- 

 sistent and consists of lenses, which frequently are workable. Near 

 Sopris, the seams " thicken and thin out characteristically," they are 

 broken by partings and the coal is dirty. Near Trinidad, the coal 

 is sometimes Avithout a parting. The accompanying rocks are as 

 variable as the coals. Near Pictou, 3 seams are mined. At the out- 

 crop, the intervals are 15 and 30 feet ; but at 2,500 feet in the mine, 

 the upper and middle beds have united and the interval to the lower 

 one is but 20 feet. The coal seams are not persistent and resin is 

 found in the northern part of the field. 



On the northern side of the Raton plateau, a sandstone at 70 feet 

 above the Trinidad coal bed. contains manv weather-beaten tree 



