58 STEVENSON— FORMATION OF COAL BEDS. [April 21. 



(listrihiilion. The granitic rocks of the northern portion thin toward 

 the south and tlieir rooted stems lean toward the south and south- 

 east ; hut the micaceous rocks of the southern portion thin toward 

 the north and the rooted stems lean in the same direction, sometimes 

 strongly. These mineral deposits interlock as wedges. But the coal 

 heds pass from one type of rock to the other, preserving well their 

 distance and parallelism. Grand' Eury finds no evidence to support 

 the delta-theory of accumulation in deep hasins ; every feature leads 

 to the helief that the mass of rocks could accumulate only hy means 

 of a suhsidence, equal and progressive from the clay hottom. 



In a still later paper, "^ Grand' Eury shows that coals of all kinds 

 are practically alike in origin. 



Coal heds are deposits of allochthonous peats formed hy an 

 exuberant vegetation, loving water, whose detritus was carried from 

 shores to interior of immense marshy lagoons, where barks, cuticles 

 and the rest were stratified with ulmic substances under the water. 

 Stipites or dry coals of the Secondary in Erance are clearly the 

 same in origin with the coals. Mineral charcoal is so abundant in 

 one of the I'pper Cretaceous coals as to give a finely-stratified 

 structure to the bed. The brown coals of the Tertiary resemble coal 

 completely in mode of occurrence; they are composed of marsh 

 plants, leaves of dry land plants being in small proportion. Lignite 

 is wood-like in appearance though formed of red humus from plants ; 

 they show much variation, but the mass of the material is derived 

 from marsh forms. The peats of lowland areas or marshy plains 

 are allochthonous — they resemble almost all deposits of mineral coal. 



Gruner*"' notes the ancient forest in the quarry of Treuil, which 

 had been described by Alex. l>rongniart many years before. At 

 100 meters lower and almost directly under the quarry, Gruner found 

 in the Treuil mine twelve great trunks in a space of less than lO 

 meters square ; their roots spread out over the coal but did not pene- 

 trate into it. 



He cannot accept the doctrine that coal consists of transported 

 material. The continuity and uniformity of coal beds make a serious 



"•'' C. Grand" I'.iiry. " Sur la fonuation dcs couclies dc liouille dc stipite, 

 dc brownkohle et de lignite," Autun, 1902, pp. 123-132. 



""L. Gruner, " Bassin houiller de la Loire," Paris, 1882, pp. 160-170. 



58 



