96 REPORT— 1876. 



Now if we suppose the gi-avelly drift to have heen deposited by the river Wharfe, 

 this must have taken place after the Glacial period, as it is clearly of newer date 

 than the two boulder-claj's. It would follow that the longitudinal slope of the 

 river-course and other conditions must first have been favourable to deposition, and 

 that afterwards the conditions changed, so as to enable the river to commence that 

 process of denudation, or carrying away, which is still going on. 



While, however, it is somewhat difficult to conceive of postglacial changes so 

 great as these, necessitated by this theory of the fluviatile origin of the gravels, 

 ■we have no clear evidences of such changes having occurred since the final emer- 

 gence of the land above the glacial sea. 



The rival theory that the gravels were deposited by the sea during the gradual 

 rise in the land accounts for their pell-mell and varied character, and for the exis- 

 tence of boulders lying at all angles. The latter may have been dropped from 

 floating ice which may still have lingered on the sm-face of the sea. 



At a considerable elevation above the channels of the Aire and Wharfe, and 

 where there is little or no clay or gravel, many angidar and subangular boulders of 

 limestone may be seen resting on Millstone-gi'it. They have chiefly been trans- 

 ported from between the north and west, and in many instances they would appear 

 to have crossed the intervening valleys and ridges. Mr. Mackintosh mentions two 

 limestone erratics near the south-west corner of Embsay Moor, at an altitude of 

 about 1100 feet above the sea. They may likewise be seen on Barden Moor, and a 

 large number have been found at Barden Reservoir, about one mile south-west of 

 Barden Tower. A few small fragments of limestone may be found resting on the 

 Millstone-gi'it of Rombolds Moor, south of Ilkley, at a height of at least 1100 feet 

 above the sea. 



On the east side of the Wharfe valley, near " Appletreewick," there is a hill, 

 consisting of Millstone-gi-it, called Symonds Seat (marked in the Ordnance Map 

 Earls Seat). On the side of this hill limestone fragments, which must have come 

 from the west or north-west, may be traced up to a height of 1200 feet above the 

 sea, but not to a greater height, as I lately ascertained. 



At High Skyi-eholme, or Trollas Ghyll, about a mile to the north of this hiU, 

 are found a most interesting series of limestone-ravines, ranging east, north-east, 

 and south-east, whose almost perpendicular sides rise 300 feet, their summits being 

 not less than 150 yards distance from each other, 1200 feet above the level of the 

 sea. On their rugged bottoms are scattered vast numbers of huge blocks of Mill- 

 stone-grit in all directions. 



The whole of this district is, geologically, exceedingly interesting. 



The author believes it may now be regarded as a fact there are no erratics on the 

 eastern slope of the north Pennine Hills in the district under notice at a greater height 

 above the sea than 1200 feet. On the western slope it is well known that they have 

 reached a considerably greater altitude. 



On the Upper iSilurian Rods of Lesmahagow. By Dr. R. Slimon. 



On the Age, Fauna, and Mode of Occurrence of the Phosphorite Deposits of the 

 So^lth of France. By J. E. Taylor, F.O.S. 



On Ridgy Structure in Coal, unth Suggestions for accounting for its Origin. 

 By Prof. James Thomson, F.R.S.E. 



Further Illustrations of the Jointed Prismatic Structure in Basalts and other 

 Igneous Rocks. By Prof. James Thomson, F.R.S.E. 



