458 STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 



The coals of the highest group vary from Fettkohle to Flamme- 

 kohle ; a single seam may yield both kinds. The Rothhell consists 

 of gray shales, hard sandstones and conglomerates with an occa- 

 sional red bed. The coals are important at St. Ingebert, but west- 

 wardly they decrease and are insignificant at the Saar River. The 

 Rischbach seams appear to be merely local, having been found only 

 in a boring and a shaft vv^ithin the Rischbach Valley. 



In the Mittelbexbach area, lo seams w^ith 9 meters of coal are 

 mined. They belong to the highest group and yield only Flamme- 

 kohle, which is an admirable domestic fuel. The mines are near 

 the siidliche Hauptsprung, where the strata are seriously disturbed. 

 The seam, Number 3, has an interesting structure in one mine. It 

 consists of coal, 0.04; parting, 0.20; coal, 1.20. The thin bench on 

 top is much broken by overthrust faults, which involve the parting, 

 but the main coal is practically undisturbed. This upper group of 

 the Lower Saarbriick becomes extremely important in the vicinity of 

 Saar River, where there are 40 workable seams with 50 to 60 meters 

 of coal. Cannel is present occasionally but it is unimportant. At 

 one place it is the highest bench ; at another it is the lowest. 



Nasse, in discussing the character of coal seams, states that in 

 this basin a seam one meter thick is rarely without partings, but he 

 mentions one, 4.08 meters, which yields clean coal throughout. 

 Variation in thickness is the rule; mere streaks become important 

 seams, which may thin away to disappearance. The intervals are 

 uncertain, so that seams widely separated at one locality may be 

 united at another. Very often the roof is Brandschiefer, a coaly 

 shale, which is combustible. When sandstone or conglomerate is 

 the roof, the upper part of the seam is irregular; but the bottom 

 rarely shares in this irregularity. 



The Ruhr Basin. — Several coal basins are in northwestern Prus- 

 sia, which are of moderate extent but, in some cases, economically 

 important. The Ruhr, Lower Rhine or Westphalian basin lies east 

 from the Rhine along the Ruhr, Emscher and Lippe Rivers; the 

 cities of Essen, Bochum and Dortmund are on the northern border. 

 The area is not far from 3,200 square kilometers, but the thickness 

 and quality of coal render it one of the most important on the con- 

 tment. The outcropping portion is south from the cities mentioned, 



