Petrography of Millstone Grit Series of Yorkshire. 745 



In Yorkshire alone, to which area for the greater part the 

 researches have been limited, the Millstone Grit forms the surface 

 of 840 square miles ; while, if that which lies beneath the newer 

 rocks and that represented by outliers on the Pennine Fells were 

 taken into account, it must have extended over at least 2000 square 

 miles. If 1000 feet be taken as its average thickness, the York- 

 shire Millstone Grit would represent a volume of 400 cubic miles, 

 the equivalent of a range of mountains 800 miles long, 1 mile 

 high, and 1 mile wide at the base. 



The beds attenuate southwards, and the only possible conclusion 

 from their stratigraphy, reached by Sorby, and later confirmed by 

 Edward Hull and A. H. Green, is that the material was derived 

 from a northern source. The evidence which the author has. 

 obtained corroborates this view. 



The ancient land-mass of the Midlands must be excluded as a 

 possible source for more than a small fraction of the material, both 

 on account of the inadequacy of the area and on account of its 

 lithological constitution. 



The Lake District was probably submerged in Visean times, and 

 for that reason could not have supplied material to the Millstone 

 Grit. Further, the abundance of monazite in these beds and its 

 absence from the granites of the Lake District, as shown by 11. H. 

 Rastall & W. H. Wilcockson, definitely exclude that area. 

 Southern Scotland ma} r have contributed to the homotaxial deposits 

 farther north than Yorkshire, but inadequacy of area is again 

 pointed out. 



Thus, by elimination of other areas for one reason or another, 

 the author shows that the most probable source of the material 

 lay still farther north in a land-mass of continental extent, of 

 which Scandinavia and the North of Scotland represent the 

 remaining fragments. In these areas alone can the mineralogical 

 demands of the Millstone Grit be satisfied, and the author institutes 

 a comparison between the Torridon Sandstone and the Millstone 

 Grit, which shows that their similarity of constitution is altogether 

 too great to be merely fortuitous. He infers that, despite their 

 disparity in age, they had a common source in that northern 

 continent. 



That continent had probably been base-levelled in pre-Millstone 

 Grit times, and the advent of this period was brought about by 

 renewed uplift rejuvenating the rivers, which removed the old 

 rotted soil-mantle and exposed fresh unleached rock. The extension 

 of the land-mass across the North Atlantic would produce a 

 monsoon type of climate, and the rock-debris broken up under 

 semi-arid conditions, as seems clear from the extreme freshness of 

 the felspars in the grits, would be swept along rapidly by floods to 

 the deltas of the large rivers. 



The author concludes by postulating one such large trunk river 

 flowing southwards from the northern continent, and receiving 

 tributaries from what are now Northern Scotland and Scandinavia, 

 debouching somewhere off the north-east coast of England, the 

 deltaic material of which (now r consolidated) forms the Millstone 

 Grit. 



