STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 147 



7 coal seams, wholly distinct and separated by thick intervals, unite 

 within 4 miles into one, 42 feet thick. Partings contain fossils ; 

 in southwestern Utah, Lee saw a limestone parting with brackish- 

 water forms ; at another locality a seam with marine limestone as 

 roof and floor has a parting with fresh-water fossils. Clay partings 

 frequently have remains of plants. 



Benches of coal beds seams often differ so much as to make cer- 

 tain that conditions were not the same during the several periods of 

 accumulation. One bench may yield caking, and another may con- 

 sist of non-caking coal ; in one, the ash may be unimportant while 

 another may be so dirty as to be worthless ; one may thin away to 

 disappearance while others overlap it. Details respecting the 

 benches are given only for districts where mining operations are 

 on large scale, but enough is known to justify the old method of 

 regarding benches as separate coal seams. 



In a general way. Cretaceous coals vary from massive to lami- 

 nated, the latter with alternating bright and dull laminae — and these 

 types are found throughout the whole section. Ordinarily, woody 

 structure is not apparent to the naked eye, but it is distinct in many 

 places. The Upper Cretaceous coal of Silesia is xyloid ; a seam of 

 Moorkohle is near Mahrens-Trubau ; the coal of the Boulder District 

 is almost as xyloid as the Eocene coals of the Dakotas ; it contains 

 logs, carbonized, jetified or silicified. Most of the Wealden coal in 

 Hannover is black and apparently without woody structure, but in 

 the same section with the black coal one finds lignitic brown coal and 

 even Blatterkohle, the latter being an accumulation of leaves and not 

 related to the Blatterkohle of the lower Rhine region. 



Few notes are available respecting microscopic structure of Cre- 

 taceous coals. V. GiimbeU'*^ studied only jet from Raschwitz in 

 Silesia and coal from the Wealden of Hannover. Woody structure 

 is well-preserved in the former ; the latter contains numerous 

 remains of leaves with clumps of wood cells and bark parenchyma, 

 all easily recognized. Thiessen"*^ examined coal from the Denver 

 Basin, probably Fox Hills. So close is the resemblance to that 



"5 C. W. V. Giimbel, Sitcb. bay. Akad. IViss., 1883, Math.-Phys. Kl. I., 

 pp. 157, 160. 



^■*6 R. Thiessen, " The Origin of Coal," pp. 241-245. 



