STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 491 



graphical disturbance. The Sama seams crop at many places where 

 faulting and folding are marked, but in Arnao and Ferrones the 

 disturbance is far greater ; the section has been overthrust and the 

 Carboniferous underlies Devonian. The coals which are richest in 

 volatile are from areas which have suffered most severely from 

 pressure. He notes, as bearing on the matter, that Gosselet had 

 shown for the Nord area in France that the northern part of that 

 region had suffered very little from disturbance while, in the south- 

 ern portion, disturbance had been violent, there being at times com- 

 plete inversion of the section. Yet coals are maigre in the northwest 

 portion, whereas in the southwest, locality of greatest disturbance, 

 one finds the fattest coals. 



Great Britain. 



The boundary between Permian and the Coal Measures is not 

 always distinct in England. The unconformity is often small and 

 it is difficult to determine a plane of separation, as rocks of the 

 Upper Coal Measures closely resemble the type, which at one time 

 was thought to be characteristic of the later period. But in consid- 

 erable areas, the case is clear, for Permian rests on upturned, eroded 

 Coal Measures. There appears to be good reason for believing that 

 the system of flexures, traceable from England across France and 

 Belgium into Prussia, originated toward end of Coal Measures 

 deposition. 



Permian deposits of Great Britain are equivalent to the Zech- 

 stein and Rothliegende of the Continent, as Murchison^° held. They 

 are absent from southern England and Wales and Hull believes that 

 that area was exposed to denudation during the Permian interval. 

 The Zechstein (Magnesian Limestone) has escaped erosion in only 

 petty areas but the Rothliegende, covering extensive spaces in sev- 

 eral fields, is thoroughly well marked, consisting chiefly of red and 

 purple marls and sandstones, with occasional conglomerates and 

 sometimes, on top, a breccia, containing fragments of trap and 

 Silurian rocks. In the South Staffordshire coal field, the thickness 



90 R. I. Murchison, " Siluria," p. 347; E. Hull, "Coal-Fields of Great 

 Britain," 4th ed., 1881, p. 524. 



