I9I2.J STEVENSON— THE FORMATION OF COAL BEDS. 441 



an extensive uplift in the northern part of the field would be suffi- 

 cient. Channels are numerous at several horizons in Indiana and 

 some of them seem to belong to a drainage system flow^ing south- 

 west, as the smaller channels enter the larger in that direction and 

 the larger ones increase in size. Non-conformity has been observed 

 at many horizons in Indiana. 



" Washouts " receive much attention in the British coal reports. 

 Some are of slight extent vertically, of a type which will be con- 

 sidered in connection with the roof of coal beds; but there are 

 others of serious importance, resembling those already described. 

 Strahan-^ states that in the Ebbw valley of South Wales, the Rock 

 Yard and Three-Quarter veins have been washed out for 1,200 

 yards on one property, a vertical cut of not less than no yards. 

 In another valley, the Rock has been removed for about a mile. 

 Scott-^ has described an old valley or estuary due to denudation 

 and removal of Coal Measures beds. The earlier Coal Measures 

 were removed and others deposited in their stead. Subsequently, 

 some of the newer beds were removed and were replaced with 

 others, also of Coal Measures age. Prestwich,-^ who long before 

 Scott had discussed this " Symon Fault," recognized that it dififers 

 notably from the ordinary washouts of coal and that the Lower 

 Coal Measures had been removed from an area of great length and 

 breadth. The work, in his opinion, may have been done by subaerial 

 denudation or by wasting currents. Fragments of coal and asso- 

 ciated rocks are not uncommon in the newer deposits. Geikie^* 

 has given among others an illustration of contemporaneous erosion 

 observed in the Coal Measures at Sanquhar, Scotland. Respecting 

 all, he is compelled to the conclusion, " rt is evident that the erosion 

 took place, in a general sense, during the same period with the 

 accumulation of the strata." De la Beche, in his "Geological 



" A. Strahan, " Geology of the South Wales Coal Field," Part II., 1900, 

 pp. 65, 68. 



^ M. W. T. Scott, " On the Symon Fault in the Colebrook Dale Coal- 

 field." Quart. Journ. Geol. Soc, Vol. XVII., 1861, pp. 457 et seq. 



^^J. Prestwich, "Geology of Colebrook Dale," Trans. Geol. Soc, II., 

 Vol. v., Part III. ; " Geology," Vol. II., 1888, pp. 98, 99. 



^* A. Geikie, " Text Book of Geology," 3d ed., 1893, P- 5o6. 



