STEVENSON— INTERRELATIONS OF THE FOSSIL FUELS. 141 



troughs but sometimes it crosses the separating ridge. Not unfre- 

 quently, there are " Sanclsacke," where the roof descends, at times, 

 even to the floor. Usually these are filled with sand or gravel but 

 sometimes with plastic clay. The coal is really in one bed, divided 

 in some places by a sandy parting. The lower portion is Knorpel- 

 kohle, but is inferior as it contains much pyrite. The upper bench, 

 though Formkohle, is a good fuel. Occasionally, a worthless, heavy, 

 sand-like dust, termed Russkohle, composes whole layers in the bed. 

 Pyrite, gypsum and retinite accompany the coal ; at one place, amher, 

 in lumps as large as one's fist, is found in the roof. Bituminous 

 wood, pressed flat, as well as silicified wood is found in many mines. 



Fiebelkorn^°® at a later date described the area examined by 

 Stohr. Like him, he recognized only one bed, which where mined 

 is from 4 to 21 meters thick and occupies a rather regular trough. 

 Occasionally another bed, about one meter thick, is seen above it, 

 the interval being filled with clay. The main portion of the trough 

 is divided into numerous subordinate troughs separated by low 

 ridges. Very often the coal is wanting on these ridges and the coal 

 in the troughs is lens-like. The coal is usually earthy in type, a 

 more or less friable mass of yellowish or reddish to dark brown or 

 black material, coarse-grained, with rather shining streak and in gen- 

 eral showing no organic texture. Toward the bottom, it not rarely 

 becomes Knorpelkohle ; but for the most part it is Formkohle and 

 on drying falls into dust. The bed contains numerous coaled stems 

 separated by spaces of one to five meters. The overlying beds are a 

 succession of white and dark sands with some clay layers, all well 

 exposed at several places where the cover is stripped. The floor is 

 usually clay but sometimes sand. It is well shown near Teuchern 

 and near Granschutz, where roots decending into it from the coal 

 are distinct. He traced these in some cases to the depth of a half 

 meter. They are those of reeds, grasses and rushes, marking the 

 floor of a swamp. 



Potonie regarded the Formkohle as, in most cases, of secondary- 



allochthonous origin. It was originally an autochthonous coal but 



had been removed and redeposited elsewhere. To this matter, refer- 



198 y[ Fiebelkorn, " Die Braunkohlenablagerungen zwischen Weissenfels 

 und Zeitz," Zeitsch. f. pr. Geologic, Jahrg. 1895, pp. 353-364, 396-415. 



