STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 75 



grain and rings distinctly. The lower part of the bed is more con- 

 choidal, less xyloid and has higher percentage of fixed carbon than 

 the upper, suggesting, as White says, that it represents a more ma- 

 tured peat. He could obtain no data respecting the floor of this bed, 

 but roots were found under two coal seams in a railway cut, the 

 sandy floor of one being undoubtedly an old soil. 



Thiessen's^^ microscopic study of the Lafayette and ^larshall 

 coals proved that, generally speaking, the type of vegetation and the 

 conditions during accumulation must have been very similar to those 

 during the Eocene in ^Montana and Dakota, though the proportion 

 of woody materials is somewhat less and the compression is greater. 

 The resin is darker than that of the Dakota lignite. The debris con- 

 tains the reticulated bodies observed in the pith of certain fossil wood 

 and present in all Tertiary and Cretaceous coals which Thiessen has 

 examined. Fungal hyphas and spores are abundant, the former 

 especially in material of herbaceous origin. Spores and pollen 

 exines compose not more than 5 to 10 per cent, of the mass. 



A notable area of Laramie has escaped erosion in the northern 

 part of the San Juan Basin within Xew Mexico and Colorado. On 

 the eastern outcrop, according to Gardner,^- coal seams are very 

 thin or are wanting; but on the western outcrop, Shaler saw along 

 the Rio Chaco several coal seams which occasionally become work- 

 able, with a maximum thickness of 3 to 6 feet. Farther north, on 

 the San Juan and Plata Rivers, he saw the Carbonero seam with 

 maximum thickness of 50 feet; but it is variable, for at one locality 

 it is little more than 6 feet and is broken by three partings. Beyond 

 the Colorado line, near Carbon Junction, the thickness increases to 

 about 100 feet; the partings are very numerous, but there are some 

 bands of clean coal. 4 to 5 feet thick. The bed divides toward the 

 west ; at 3 miles southeast from Durango, Shaler saw three seams, 

 7, 30 and 15 feet, in a vertical space of less than 200 feet, which he 

 believes to be splits of the Carbonero. 



Apparently no part of the Laramie has escaped erosion in the 

 great Uinta Basin of northwestern Colorado; or. at least, if any 

 still remain, its rocks are so similar to those of the Pierre that no 



31 R. Thiessen, Bur. of Mines, Bull. 38, 1913, pp. 241-243. 



32 J. H. Gardner, Bull. 341, 1909, p. 388; M. K. Shaler, Bull. 316, Pt. 2, 

 1907, pp. 385, 386, 395, 396, 400, 404. 



