STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 479 



is double with a parting, o to 8 meters thick. The coal thickens and 

 improves in quality toward the west, becoming 5 meters near Grand- 

 'Croix, where the benches are united. The roof of the upper bench 

 is sandstone and erosion of the coal is frequent ; but that of the lower 

 bench is shale and the coal is always regular. Two lower seams 

 have poor coal; one has maximum thickness of 1.40 meter near 

 Grand'Croix, but the other is a lens, disappearing in all directions. 



Beyond the Rive-de-Gier, one reaches the sterile stage of St.- 

 Chamond, 500 to 800 meters thick, the lower portion a coarse con- 

 glomerate, the upper less coarse and micaceous. The upper or 

 micaceous division is thin at southeastern localities but it increases 

 at expense of the lower portion until, near St.-Chamond, it has re- 

 placed it almost wholly. Thin coal seams occur in the area of coarse 

 deposits but they disappear when the micaceous beds predominate. 



The Stage de St.-fitienne inferieur, 850 to 950 meters thick, has 

 10 to 12 coal seams, some of which occasionally divide. They vary 

 abruptly in thickness as well as in quality of the coal. Seams 8 and 

 12 at times yield excellent coking coal but at others they are so dirty 

 as to be worthless. Coal seams are regular where the rocks are 

 quartzo-feldspathic but become worthless or disappear when the 

 rocks are micaceous. The upper division has one important seam, o to 

 6 meters thick, which suffered much from contemporaneous erosion, 

 having been removed wholly in many places. The coal is good for 

 coke, though it must be washed to remove the high ash. The coal of 

 this stage was formed of Cordaites, Psaroniocaulon, Aulacopteris 

 and Calainites. 



The Middle stage of St.-fitienne, about 350 meters thick, has 8 

 or 9 coal seams separable into two divisions ; the lower has two 

 seams. In the upper, Nos. i and 2 have inferior coal containing 

 kidneys of iron ore and trunks of trees, replaced with carbonate of 

 iron. Ordinarily they are not mined, but No. 2 occasionally becomes 

 3 meters thick and has good coal. Nos. 2 and 3 are united at many 

 places ; the latter averages 4 to 5 meters ; No. 4 is ordinarily at 20 

 meters below 3, but the interval varies from o to 24 meters. At 

 times, No. 3 is 10 and 12 meters thick, but in such cases it consists 

 of I, 2, 3 and 4 united. The coal of this stage originated from the 

 same plants as in the Lower St.-£tienne. 



