THE GLACIAL PERIOD. 203 



are twisted, abruptly truncated, displaced, and fantastically 

 jumbled, in such a way as to suggest that the deposits have 

 been dragged forward under great pressure. In the sections 

 given by him to illustrate the aspect assumed by the disturbed 

 Oligocene strata, it may be observed that the contorted coal-beds 

 are bent over in one determinate direction, thus indicating the 

 path followed by the disturbing agent. 1 



These and other appearances bear testimony to the enormous 

 pressure exerted by the ice-sheet, and are totally inexplicable 

 on the iceberg-hypothesis. "We have, in short, every reason for 

 concluding that the northern mer de glace advanced as far south 

 as the most southerly limits reached by the great " Northern 

 Drift." 



Upon the map of Europe (Plate D) which accompanies this 

 volume, I have indicated the area covered by the ice-cap — the 

 southern boundary -line corresponding very nearly with that 

 which Murchison and his colleagues have given, 2 as the ex- 

 treme limits reached by the " erratic formation." The fine 

 lines are meant to show the principal directions in which 

 the upper strata of the ice flowed. These, as a rule, correspond 

 to the average trend of rock-striations, roches moutonne'es, and 

 the carry of the stones in the till. In other words, the whole 

 body of the ice pressed forward in certain general directions. 

 Nevertheless, there is abundant evidence to show that the 

 under strata of the ice, influenced by the configuration of the 

 ground, frequently moved in directions quite at variance with 

 what must have been the flow of the upper strata. The long 

 bent red arrows upon the map indicate the trend of the lower 

 strata in one or two places. Upon a larger map more might 

 have been inserted, but those given will sufficiently illustrate 



' Zeitschr. deutsch. geol Oes., 1880, p. 75. Credner's paper contains numerous 

 references to the literature of this interesting subject, and gives by far the most 

 complete account of the phenomena which has yet appeared. The facts brought 

 forward by him appear to me sufficient of themselves to demonstrate the sub- 

 glacial origin of the till, and to show that Saxony was formerly overflowed by the 

 great mer de glace. 2 Geology of Russia and the Ural. 



