part 4] THE MILLSTONE GRIT OF YORKSHIRE. 283 



seems evident from the fact that this region, from Devonian right 

 through Carboniferous to Permian times, was the Locus of intense 

 volcanic action. Oscillations of level and unequal subsidence are 

 the concomitant features which we naturally find in such an area. 

 This line was, it would seem, the limb of a great earth-fold, and 

 the line of weakness so determined gave rise to the volcanic action 

 cited above, as in similar circumstances we have lines of volcanoes 

 to-day. Generally, then, the physiography of the opening stages 

 of the Millstone Grit period may be represented by saying that 

 folding was again taking place along the old Caledonian, axes, 

 bringing into existence a great earth-wave, the crest of which is 

 represented by the Northern Continent and the trough by the 

 South of Scotland, Ireland, and the North of England. That 

 successive uplifts went on during Millstone Grit times is traceable 

 in the fact that we have coarse beds at the base (Kinderscout), 

 liner material in the Middle Grits, and coarse again in the Rough 

 Rock, and in the Coal Measures we note again the tine-grained 

 detritus succeeding the Rough Hock and comparable with the 

 Middle Grits. It is most remarkable that the dominant consti- 

 tuents, both of the larger fragments and the smaller grains, should 

 be the same in the Kinderscout Grit and in the Hough Hock, 

 showing that the main source of supply must have been the same 

 in both cases. With regard to the height to which the land was 

 ridged up in the Northern Continent there is no definite evidence, 

 but it must have been considerable, in order to cause so great a 

 condensation of moisture as it is absolutely necessary to predicate, 

 in order to supply the volume of water for the large rivers which 

 transported the detritus of the Grit and Coal Measures, and it 

 would indeed seem to me that the relief of the land must have 

 been of Himalayan grandeur. 



XI. Drift- or Cuebent-Beddistg in the Grit. 



As was pointed out by Dr. Sorby, in the paper already cited, 

 trustworthy information as to the direction from which the 

 material composing deltaic deposits has been brought by the 

 rivers is afforded by an examination of the drift- or current-bedding 

 to be found in all such deposits. It must be remembered that, in 

 applying such a test, absolute agreement in the compass-bearing of 

 such bedding, either in the same vertical section or over any wide 

 area, is not to be expected, but some prevalent direction must 

 emerge when a sufficiently large number of readings are taken. 

 Suppose, for instance, a great river with a correspondingly extensive 

 delta, such as the modern Mississippi. In lowing over its delta 

 the distributaries will carry forward material in directions which 

 make a considerable angle with the main river and with each other, 

 as in the diagram (fig. 3, p. 284), and the angle between the two 

 outermost distributaries may exceed 180°. Moreover, these distribu- 

 taries have meandering courses, which further complicates matters. 

 Nevertheless, in the compass-bearing of the current-bedding 



