Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/161

Rh Junction; the river under the viaduct is 325 feet above the mean level of the tide at Liverpool. The rails of the Taff-Vale line are 96 feet above the Taff at Quaker's-Yard Junction, and 30 feet at Aberdare Junction, so that the rails are laid on a very steep incline of 1 in 50. On the average, between B and C the fall of the rail is 154 feet, and that of the river about 88 feet between the two stations. The rails cross the river on a viaduct about 96 feet high near the upper end of the incline, and on a bridge 30 feet high at the bottom of the incline.

The section given in Pl. IV. fig. 1 commences at Quaker's-Yard Junction with a bed of loose gravel lying along the sides of the valley, 140 feet high above the river, but probably not of greater thickness than 40 or 50 feet on any part of the rock out of which the sloping sides of the valley are excavated. The gravel is full of very large boulders of the local Carboniferous rock, which is an extremely hard, compact, massive-bedded sandstone of the Pennant series, several hundred feet thick. These boulders are sometimes angular, and sometimes weathered or rolled. There also occur quantities of Mill-stone-grit, brought ten miles down the valley of the Taff, these being always rolled, and boulders of limestone, with a small but conspicuous percentage of well-rolled pebbles of Old Red Sandstone from the Brecon Beacons and other distant hills. These red pebbles are still more worn and rolled than those of the Limestone and Millstone-grit, the source of which is nearer to Quaker's Yard than the Old Red Sandstone. The matrix is clay and sand derived from the Coal-measures, or from decomposed Millstone-grit.

After passing the viaduct, Pl. IV. fig. 1, the section is continued