STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 



459 



but borings prove that the coals persist northward beyond the Lippe 

 under increasing cover and that, in like manner, they are present 

 west from the Rhine. The region has been studied carefully by 

 Dannenberg,^" who has supplemented his observations by those of 

 other geologists. 



The Lower Carboniferous (Dinantien) is shown on the eastern 

 border, where it is succeeded by the Flotzleeren Sandstein (Namu- 

 rien or Lower Westphalian), which apparently is without coal and 

 is taken to be the equivalent of the Millstone Grit, the Sudetic of 

 eastern areas. This is followed by the Productive Coal Measures, 

 equivalent to Saarbriick (Upper Westphalian), as well as to the 

 Lower and Middle Coal Measures of Great Britain, It is the im- 

 portant group. The Ottweiler, Stephanien of France, is apparently 

 absent. Permian is represented almost wholly by the Zechstein, 

 Rothliegende having been observed in only a few petty, isolated 

 patches. The Saarbriick is in four divisions, which, in descending 

 order, are : 



There are variations in the conditions for, chemically, the coal of a 

 seam is not the same throughout its extent. Beds of the Mager- 

 kohlengruppe at times yield coking coal; among the Fettkohlen- 

 gruppe, some give gas coal while coking coal is obtained from sev- 

 eral seams in the Gaskohlengruppe. Generally speaking, the volatile 

 content increases from west toward east, as does the thickness of 

 the seams. Conglomerate and ironstone are common in the Mager- 

 kohlen, less so in the middle divisions, but are abundant in the 

 upper. Marine deposits are frequent in the lowest division, but 

 become fewer above, where fresh-water fossils are the usual forms. 

 The Magerkohlengruppe is practically barren in the lower 250 

 to 300 meters, there being only thin seams, some of which are work- 

 able locally. The next portion, reaching to the Hauptflotz, has at 



5" A. Dannenberg, "Geologic der Steinkohlenlager," 1908, pp. 49-79. 



