470 STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 



v;as extreme. In four important seams of the faisceau Seraing, the 

 percentages at the north are 13, y.},, 6.2, and 6, but these increase 

 southwardly to 20.8, 18, 15.5, 16.6. 



France. — Passing into the Department du Nord in France, one , 

 reaches the Valenciennes basin, which is continuous with the Hainaut 

 basin at the east and with that of Pas-de-Calais at the west. Ac- 

 cording to Barrois, the Coal Measures come to the surface in a corn- 

 paratively small area near the Belgian border but elsewhere they are 

 largely covered by later formations, so that mining operations were 

 begun at much later date than in Belgium. During Trias, Jura and 

 Lower Cretaceous time, the Coal Measures were exposed, and ero- 

 sion removed them from a great area. The limits of the coal de- 

 posits have been determined approximately by borings, but the region 

 has been disturbed so seriously by folds and overthrust faults, espe- 

 cially along the southern border, that the succession can not be 

 determined beyond doubt. The basin is from five and a half to six- 

 teen kilometers wide. The coal seams are numerous, fairly uniform, 

 but are thin, rarely exceeding" one meter and averaging about 70 

 centimeters ; under favorable conditions, some only 35 centimeters 

 thick, have been mined. The actual number of workable seams can 

 hardly be determined ; Olry attempted to ascertain it. Going from 

 north to south, he found in the several faisceaux, beginning at the 

 bottom, 



A, in the northern portion, 



faisceaux i, 2, 3, 35 seams ; 4, 31 seams ; 5, 36 seams ; 



B, in southern portion, 



6, 25 seams ; 7, 16 seams ; 8, du Marly, 3 seams, in all 146 seams. 

 But paleontological work by Barrois and Paul Bertrand^'' has proved 

 that this number is much too great. The seams appears to be su- 

 perimposed as Olry supposed them to be, and the change in chemical 

 composition is singularly regular in the order ; but certain seams 

 have been recognized in both portions of the region, though differing 

 in facies and in composition. Barrois states that the seams of fais- 

 ceaux I and 8 must be ignored, that faisceaux 5 is superimposed only 



^3 C. Barrois, " Expose de I'etat de connaissance sur la structure 

 geologique du bassin houiller dans le Department du Nord," Lille, iQog, 

 pp. 1-22. 



