118 STEVENSON— FORMATION OF COAL BEDS. [April 18, 



the roof; one notable case being that of the couche Grande Moisa, 

 near Liege, where the coal is so distorted as to be thrown into a suc- 

 cession of hook-like curves. Briart^-' has given illustrations of 

 similar movements in coal beds of the Nord basin. He had ob- 

 served the phenomenon also in Italy just be3ond the Austrian border. 

 There one finds boghead, with clay beds, between great strata of 

 dolomite, the latter showing throughout the section a remarkably 

 regular dip of 30 to 40 degrees. Aside from this dip, they show no 

 signs of disturbance, but the intervening, yielding rocks have been 

 thrown into complicated folds. Katzer^-^ notes a peculiar case; the 

 upper part of a coal bed has been pushed into complex wrinkles, 

 which occasionally affect the whole bed ; but there are no wrinkles in 

 the roof. Strahan,"" in referring to a contorted clay parting between 

 undisturbed benches, remarks " obviously the shale acting as a lubri- 

 cant, has permitted differential movement between the strata above 

 it and those below it." The explanation is manifest everywhere and 

 is not open to dispute. 



I . The Hypotheses. 



The reader who has examined Part I. of this work has dis- 

 covered that, in most cases, an author regards his hypothesis as 

 wholly satisfactory, as explaining all phenomena deserving explana- 

 tion. The allochthonist greets joyfully each occurrence of pebbles in 

 coal, of land shells in the rocks, of rooted stumps filled with sand, 

 etc., as so much additional evidence in favor of his doctrine ; while 

 the autochthonist is equally elated by such occurrences, which are 

 infallible proofs that his doctrine is correct. Observations at given 

 localities are often contradictory, but there is no reason to assume 

 that any observer has asserted, knowingly, an untruth or suppressed, 

 consciously, a truth ; yet it is clear that, in some cases, personal 

 equation has played an important part, there being, apparently, 



"'A. Briart, "Notes sur les mouvements paralleles des roches stratifiees," 

 ibid., pp. 129^135. 



"** F. Katzer, "Notizien zur Geologic von Bohmen," J^erli. k. k. Reichsanst., 

 1904, pp. 150-159- 



'"' A. Strahan, " Geology of South Wales Coal-Field," Part V., 1904. 

 pp. 65, 66. 



