Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/157

Rh The gravel is 50 feet above the river Aire in the thickest part; and no rock has been met with to prove how much lies below the level of the river-bed; but the town surveyor, who has carried out the drainage of that town, informs me that the rock is probably from 30 to 40 feet below the level of the river.

Considering the width of the valley, nearly three-fourths of a mile, we might estimate the gravel over a width of 1000 yards to be of an average thickness of 20 yards; 20,000 yards at a weight of 1$1⁄2$ ton to the cubic yard, is 30,000 tons; there would be then 30,000 tons of rock and gravel to each yard run, or about 53 million tons of gravel to each mile of river, supposing the section, fig. 3, at Bingley to contain the average amount of gravel in that valley.

This quantity of 53 millions of tons of gravel per mile is apparently not out of proportion to the power and dimensions of a river able to flood its valley to a height of 50 feet over a surface a mile wide with a gradient of from 3 to 10 feet per mile.

The escarpments, or gravel-banks, 50 feet high and 200 yards wide, in fig, 4, appear to mark the ordinary limits of the ancient river, as the sides of the gravel-bank are laid in many parts in the form of a steep escarpment sloping to the current at an angle of from 25° to 35°, while the top of the gravel-bank is flat, except where it is hollowed out by another part of the river-channel more or less deeply. A bank of 10 feet above the Aire is sufficient now to retain the water, except in the heaviest floods. Contrasting the floods of this river at the present time with those in. the period when the gravels were deposited, it would appear that a flood-lines of 10 feet now replaces one of 50 feet. The cubes of these flood-lines would probably represent the proportion of the volume of water flowing down the valley in the two cases. Then 103 is to 503 as is 1 to 125. The volume of water would on that hypothesis now be only the $1⁄125$ of that in the gravel-period.

Section (Pl. IV. fig. 5) along the line C D, through Rye-Loaf Hill, one mile E.S.E. of Bingley, shows the outline of the gravel-deposit lying on Carboniferous sandstone and shales. This part of the Aire gravel, along the line C D, reaches also to a height of 50 feet above the present level of the river; it does not appear to have ever been worked for limestone, and is about the same height above the irverriver [sic] Aire as in A B. The escarpment of the gravel at Rye-Loaf Hill is well marked, and slopes to the river at 25°; the top is flat, and the form such as could only be produced by a river occupying during floods the whole width of the valley, the water rising at least 50 feet above the present flood-level. The limestone boulders forming a large portion of the Bingley gravel are so well rounded that they indicate long-continued rolling in a river-channel.

There is a swamp to the east of Bingley church, in which remains of oak-trees have been found in peat, and below the surface a stratum of freshwater shells of existing species, according to my informant. This part of the section appears to be identical with the Hippopotamus-bed at Leeds.

Mr. A. Harris, jun., of Ashfield, found, in 1868, pieces of rolled