380 ANNALS NEW YORK ACADEMY OF SCIENCES 



l)y which not only the Permian, but also the underlying deposits, were 

 removed from the southeastern and eastern portions. The relations of 

 the strata throughout indicate that all of the beds, mineral and organic 

 alike, had at one time a much greater extent than now. One cannot be 

 far wrong in estimating the original extent of the Campagnac coal bed 

 as at least 12 square miles, almost all of it on the eastern side of the basin. 

 The thickness of the coal varies, but one is safe in taking it as 35 feet, 

 that being the least reported in any locality where work has been done in 

 recent years and from one half to one third of that observed or reported 

 in localities where work is now in process. Almost the whole of the 

 eastern half of the basin was covered by a coal bed from 10 to 90 feet 

 thick and averaging not far from 35 feet. 



The extent of the Bourran bed was greater. It covered the whole of 

 the eastern area, as is shown by the preservation of the Firmy block as 

 well as by the distribution of Permian beds. The Permian covers the 

 Bourran deposits along the central strip, but the Bourran coal crops out 

 on both sides of that strip. The thickness is greatest in the central por- 

 tion of the basin, but it is still great on the eastern border at Firmy, while 

 at the extreme south, as at the extreme north, it becomes irregular and, 

 though still thick, is broken by many shale partings. On the western 

 side of the syncline south and west from Cransac, it is much thinner than 

 at tlie eastern outcrop, while at the south on that side, shale partings in- 

 crease at the expense of the coal. The thinner, irregular beds in the 

 western part of the basin are contemporaneous with some part of the 

 great Bourran bed, and it may be that the bed was practically continuous 

 over the whole basin ; but owing to the energetic erosion, evidence to sup- 

 port that suggestion cannot be obtained. One can only take the area as 

 approximately 20 square miles, confined to the eastern two thirds of the 

 basin. The minimum thickness reported is 18 feet; from that it ranges 

 up to more than 100 feet, so that one is not in danger of exaggeration, if 

 he regard the area as covered originally by the equivalent of 35 feet of 

 coal. 



The section of the Campagnac coal bed, obtained at the Tramont de- 

 couverte, closely resembles that of the ordinary bed with underclay and 

 with clay partings throughout ; but no such section of the Bourran bed is 

 available, for in the Decazeville decouverte, the coal has been faulted and 

 folded within the bed to such an extent that one cannot detennine 

 whether or not any of the inclosed clays was continuous, but there is 

 ample underclay. ISTo impressions of Stigmaria were seen anywhere, so 

 that neither Lepidodendron nor Sigillaria contributed materially to for- 

 mation of the coal. 



