74 STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 



mined in the Lafayette district, is 14 feet thick at the outcrop ; but 

 within 500 feet a parting appears, which increases northwardly to 

 10 and at length to 25 feet. The splits remain good in this direc- 

 tion, but southwardly, as the parting increases, the lower split is 

 broken more and more by slates until it becomes worthless. The 

 coal in some seams is not the same throughout ; one bench may be 

 hard, another soft. In one bed, the upper bench yields softer coal 

 than the lower, which is complex, consisting of : Bright coal with 

 conchoidal fracture, 6 inches ; crushed coal, 6 inches ; fibrous coal, 

 36 inches. The coal of the Denver Basin often has woody struc- 

 ture and contains silicified tree trunks, knots and branches. It is 

 resinous at many places. 



D. White^° states that, while the coals of this Basin are relatively 

 persistent, they vary greatly in thickness. The topography of the 

 floor reveals shallow " swales " or ponds, occasionally extending a 

 mile or more, in which the coal is thicker. The floor at Lafayette is 

 a bluish sandy underclay, containing numerous roots in place, prob- 

 ably an old swamp soil; resting on this is a bed, 8 to 30 inches thick, 

 of dark carbonaceous clay, or lignitic mud, filled with flattened stems, 

 lying in all directions, some of them very large and many are much 

 compressed. The roof is sandstone with no transition from the 

 coal. 



In general, the coal is essentially xyloid, there being apparently 

 more wood than in the lignite of Hoyt and Rockdale in Texas, 

 though less than in that of Wilton and Lehigh in South Dakota — 

 all of them Eocene. The quantity of jetified wood is large but the 

 branches and limbs are compressed to thin lenses. Mineral charcoal 

 is abundant, often in large fragments. A log was seen, 14 by 5 

 inches in section, jetified in the interior, while the outer portion had 

 become mineral charcoal ; but another specimen was hollow, contain- 

 ing mineral charcoal in the interior, while the outer portion was 

 jetified. Irregular lumps of yellow resin are numerous and at times 

 this material has been squeezed into the joints. 



The coal at Marshall, 10 miles from Lafayette, is at the same 

 horizon, being regarded as one of the splits of the main Lafayette 

 seam. Silicified wood is abundant and well-preserved, .showing 



30 D. White, "The Origin of Coal," Bur. of Mines, Bull. 38, 1913, pp. 20-23. 



