460 STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 



least two workable seams and is loo meters thick. The Hauptflotz 

 and the Wasserbank, 8o meters lower, have well-marked marine 

 roofs ; between the Hauptflotz and the Mausegatt, 250 to 300 meters, 

 coal seams are few and but locally workable; the Sarsbank, about 

 midway, has a marine roof. The next interval, 100 to 150 meters, 

 has four or five workable seams with 3 to 4 meters of coal and con- 

 tains much iron ore, which was mined in earlier days. It has three 

 beds with fresh-water fossils. The highest interval, about 300 me- 

 ters, is almost barren, having few and rarely workable seams. The 

 most notable feature is the rich marine roof of the seam Finefrau- 

 Nebenbank near the base of the interval. This Gruppe ends with a 

 well-marked conglomerate, 10 to 20 meters thick. 



The Fettkohlengruppe, from the Sonnenschein to the Catharina, 

 averages about 600 meters, but the mass increases toward the east, 

 coal increasing in the same direction from 23.6 to 35.85 meters. 

 Clay shales predominate, sandstone is rare and conglomerate is un- 

 known. Ess- or Schmiedekohle, with about 20 per cent, of volatile, 

 predominates in the lower part, but in the upper part the volatile 

 becomes 33 per cent, and the coal is caking. The coal seams tend 

 to divide, detracting from their value. Catharina alone is easily 

 identified in a considerable area, as it has a marine roof. 



Changes in most of the seams are so abrupt that tracing is im- 

 possible ; mere smuts suddenly become workable seams and as sud- 

 denly become worthless again. 



The Gaskohlenpartie is almost barren in the lower half, but the 

 upper portion has about 10 workable seams with 8 meters of coal. 

 The lower part has a seam of cannel, 47 centimeters thick. Changes 

 in chemical composition of coal in individual seams are frequent. 

 No marine forms have been discovered except at the very base, in 

 the roof of Catharina. 



The Gasflammekohlengruppe has 25 seams more than 50 centime- 

 ters thick. Clay shales predominate in the lower half and the coal 

 seams are much less variable than those in the upper half,, where 

 sandstone and conglomerate prevail. Chemically, the coal varies 

 notably; in extensive districts, only gas coal is found. Cannel oc- 

 curs frequently; one seam has 1.36 m. as the upper bench and 1.37 

 m. as the lower. 



