164 STEVENSON— INTERRELATIONS OF THE FOSSIL FUELS. 



lumjDs of amber-like resin, some of them apparently still attached to 

 the wood. At the bottom of the bed there is a thin layer of dirty 

 lignite. 



The coal at Lehigh, North Dakota, is in the upper portion of the 

 Fort Union, and the bed mined there is but one of many, 20 seams 

 having been counted in one short section. ]Most of these had been 

 laid down in freshwater swamps ; usually they rest on underclays 

 and frequently they have clay partings. The thickness is reported as 

 varying from 6 to 8 and even more feet, " the greatest developments 

 being found in the hollows of the floor, the coal thinning on all 

 sides to the ' rise,' though on the whole it is relatively regular in 

 bedding and thickness." The bed is singularly clean. The lower 

 bench is free from all partings, except the charcoal layers, which are 

 apt to be sulphurous. It is a dark brown, earth-colored lignite in 

 which the large amount of wood is noteworthy. The grain of the 

 wood is conspicuous as are also compressed trunks of trees with 

 their branches, which compose about 75 per cent, of the whole. 

 Some logs are gnarly, one to two feet wide and several inches thick. 

 Some fragments are fully jetified, others partly so and others still, 

 not at all, aseptic conditions having prevented decay. There seems 

 to be little resin. The roof and floor could not be studied, but roots 

 were observed in underclays of some higher beds. 



Thiessen--^ studied the coals of Montana and North Dakota, col- 

 lected by D. White. They are all xyloid lignites, consisting of 75 to 

 85 per cent, of woody material. The interstices are filled with 

 debris from a large variety of plants and parts of plants, a binding 

 stuff or " Fundamental matter." This semi-decayed, macerated, dis- 

 integrated material, composed of wood, parts of angiospermous and 

 gymnospermous leaves, herbaceous stems, bark, roots, exines of 

 spores, pollen, resinous and waxy bodies, cuticles, is cemented by 

 matter, which apparently was once plastic. Spores and pollen exines 

 form a considerable portion of the mass. The trunks of trees are 

 wholly of conifers, mostly Taxadinese and Cupressinese, with a few 

 Abietinese, there being no stems certainly recognizable as dicoty- 

 ledonous. 



He compares the conditions with those observed by him in peat 



229 R Thiessen, " Microscopic Study of Coal," pp. 221-232. 



