Page:Quarterly Journal of the Geological Society of London, Volume 24.djvu/214

104 Fifthly, that the height of 70 feet, at which fossiliferous gravels now stand above the level of the Somme, is much beyond the limit of floods, and therefore that these gravels could only have been deposited at St. Acheul before the river-channel was cut down to its present level.

The general effect of these assertions was to refer the remains of man found in St. Acheul back to an indefinite date, separated from the historical period by an interval during which valleys were excavated or deepened 40 or 50 feet.

In a paper read before this Society in April 1866, I suggested that there was evidence of very little weathering or atmospheric action since the date of the drift containing human remains, and that the age of these deposits was close to the Historical period,—also that the upper and lower valley-gravels in the Somme were continuous and of one period.

I afterwards read, in June 1866, a statement of what I believed to be the correct interpretation of the Amiens and Abbeville sections, reasserting the continuity of the gravel-deposits on gradual slopes from the higher to the lower levels in the valley, except in rare cases or isolated spots, where the continuity was interrupted or prevented by some upstanding piece of the original rock out of which the valley had been cut, in which case the gravel wraps round the base of the upstanding knoll of chalk. I quoted the section at Montiers as one that shows a direct sequence of gravel from above the railway to the Somme, notwithstanding the version of that locality published by Mr. Prestwich, in which chalk is represented in a position where I could only find gravel.

At the same time attention was drawn by me to the probability of the brick-earth terrace sloping down to the Lea Marshes at Clapton being of the same age as the similarly formed Loess terrace sloping down to the Somme at Amiens. I also asserted that there was good evidence in the direction and gradient of the terrace, in the configuration of the gravel and brick-earth and of the London-clay surface at Clapton, of the water having occupied the whole valley of the Lea at the time of the formation of this Clapton terrace, and also of the water of the river Lea or other rivers having reached very much higher levels in the vicinity at that period, while the Stoke-Newington and Highbury gravels and brick-earth were being deposited.

I still hold these opinions, and am prepared to demonstrate their truth; and I ask the attention of the Society to a restatement of the exact geological facts to be seen in the Somme valley, and to evidence quite independent of that which has been previously submitted to the Society, although to a certain extent going over the same ground.

The conclusions that I arrive at are extremely dissimilar to those of Mr. Prestwich and Sir C. Lyell, and are as follows:—

First, that the surface of the chalk in the valley of the Somme had assumed its present form prior to the deposition of any of the