Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/160

66 associated with the works of man near Bedford, Abbeville, Salisbury, and other localities, so that we are enabled to correlate the gravel of the river Aire with that of a number of rivers which appear to have risen in times of floods from 40 to 80 feet above their present ordinary level in that part of the Quaternary period which I term the "Pluvial period" (Quart. Journ. Geol. Soc. vol. xxiv. pp. 105, 120).

The Cyrena fluminalis or consobrina is found in the gravels abundantly at St. Valery, at the mouth of the river Somme, in Picardy, and also in the estuary of the Humber at Kelsey Hill. The Aire flows into the Humber.

There is, as might be expected, great difference in the materials of which the respective gravels are composed, arising from the different character of the rocks over which the rivers flow, and from the greater fall of the Aire in its course, from its source to the sea, than that of the Somme. The important stratified valley-gravel at Abbeville, containing numerous species of shells, is represented by the Kelsey-Hill and Hessle beds near the mouth of the Humber at a similar height above the river. The width of the valleys is not so different as their depth; but this is due, as before stated, to the difference in the fall of water per mile in the two rivers Somme and Aire.

There is no good section of gravel now open at Bingley. The limestone boulder-pits have been filled up many years; and the railway is carried near the present river, or in an old secondary river-course of the gravel-period.

I shall now describe some measured sections of very thick and important river-gravels in the valleys of the rivers Taff, Rhondda, and Cynon, in Glamorganshire, South Wales.

A longitudinal section of the river Taff would show the rapid character of the river, which falls nearly 500 ft. between Merthyr Tydvil (A, fig. 3) and the sea at Cardiff, about twenty miles. The following heights of the bed of the river Taff, above the coping of Bute Dock, Cardiff, were kindly furnished me by Mr. George Fisher, Engineer in chief, Taff-Vale Railway. These heights were the only ones sent to me relating to the river Taff. Their exact position on the map was also laid down by Mr. Fisher himself, and fig. 3 is a carefully reduced copy of his map. The coping of Bute Dock is 9⋅82 ft. above the level of ordinary spring tides.

Plate V. is a plan of the river Taff, near Quaker's-Yard Junction. Pl. IV. fig. 1 represents a long section opened out by the Taff Vale Railway (A B C), the position of which is shown on the plan (Pl. V.). The heights at different points have been kindly determined by Mr. L. T. Lewis, F.G.S., of Aberdare, or by Mr. G. Fisher, of Cardiff, and are marked on the section.

The plan and section of the valley of the Taff, between Quaker's-Yard Junction and Aberdare Junction of Taff Vale, represent about one mile in length by two-thirds of a mile broad. The height of the point of the sandstone-rock forming the crown of the hills is about 275 feet above the level of the Taff at Aberdare