Page:Quarterly Journal of the Geological Society of London, vol. 32.djvu/258

186 granite, silurian porphyritic greenstone, and other foreign pebble's occur; and at and below this point examples of these rocks may be detected in the bed of the river wherever gravel is exposed. This is situated at an elevation of about 200 feet above the sea level.

At the Elland railway-station, the following section has been exposed by some recent operations of the Company:—

At the cemetery, a few hundred yards to the north-west of the last-named place, and at an elevation of about 300 feet, a bed of gravel, sand, and loam, varying in thickness from 5 to 10 feet, analogous in character to the section last described, reposes upon the Carboniferous shale. And in the Shibden valley, deposits precisely similar to these are found at about a corresponding elevation.

In the three last-named instances the stones composing the gravel consist of well-rounded waterworn rocks, derived exclusively from the basin of the Calder and its tributaries, not a foreign pebble being found incorporated with them. This gravel may therefore be regarded as having a purely local origin, and probably dates from the time when the river ran at this level, and is consequently in no way connected with the glacial drift which occurs in the valley below.

Precisely analogous conditions to those already described as occurring in the Walsden defile exist in the Cliviger valley, the drift running up on the sides of the hills near the entrance of the gorge to a height of 1075 feet, its southerly termination taking place both on the sides of the hills and in the valley in a line almost corresponding with the summit-level of the latter at Calder Head, which has an elevation of 768 feet.

It appears from a paper read some time ago by Mr. R. H. Tiddeman, of the Geological Survey, that a very similar state of things occurs with regard to the distribution of drift in the great watershed of the north, opening between the basins of the Ribble and the Aire, which has a summit-level of 700 feet. No ice-scratches are shown on the excellent map which accompanies that paper as existing east of the watershed of the Pennine range in that part of the country; and those which do occur near to that line run, with one exception, in a direction closely approaching to north and south.