482 STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 



stumps are involved in a maze and he has observed cases where the 

 roots of one stump penetrate stumps at a lower horizon. Some long 

 roots cross several layers of subjacent rock. He is convinced that 

 the fossil forests were developed sur place. 



Commentry. — The petty basin of Commentry, though embracing 

 barely six square miles, is perhaps more familiar to geologists than 

 is any other of the Plateau basins, St.-£tienne alone excepted. It 

 v/as studied during many years by Fayol,''^ who described it in an 

 elaborate memoir and utilized the results as basis for his well-known 

 Delta hypothesis. This memoir is so detailed and contains so much 

 of interest that it is difficult to prepare a synopsis of the facts bear- 

 ing on matters concerned in this study. 



The basin is a depression in Archean and apparently contains no 

 rocks older than the higher Carboniferous. It is divided into five 

 strips, extending from north to south : Bourdesoulles, at west, con- 

 taining coarse rocks ; Le Marais-les Ferrieres, sandstones, shales and 

 coal seams ; Montassiege sandstones and blocks of rock ; Les Pe- 

 gauds, sandstone, conglomerates, shale and coal seams ; Longeroux, 

 at east side, conglomerates. Montassiege separates the sub-basins 

 of Les Ferrieres and les Pegauds, which together make up barely 

 one third of the whole area and in each case have only a very small 

 space occupied by coal. The coarser rocks predominate throughout, 

 shale and coal being only 4.5 per cent, of the whole mass. 



The important coal deposit of les Pegauds has an outcrop rudely 

 resembling the capital letter C. At the easterly extremity, it begins 

 as a single seam of insignificant thickness, but increases along the 

 curved outcrop, dividing and at last thinning away to disappearance 

 on the east side of Montassiege, where it is represented by 8 thin seams 

 within a vertical section of 200 meters. Southwardly within the 

 curve, it dips at o to 50 degrees and finally comes to an end at a depth 

 of 350 meters. Near Longeroux, at the east, the thickness is only a 

 few centimeters, but at the northerly part of the outcrop, the main 

 portion, known as the Grande Couche, averages between 10 and 12 

 meters for a distance of 2.5 kilometers. Thence westwardly it de- 

 creases to disappearance. The coal for the most part is caking and 



S3 H. Fayol, " fitudes sur le terrain houiller de Commentry," Liv. prem. 

 St.-fitienne, 1887. 



