V.—The Brookwood Deep-Well Section

Extract

This section, which was completed last year, appears of such value and interest to students of the Tertiary strata of the London Basin, that I have thought it worth while to offer a description of it to the readers of the Geological Magazine. Through the courtesy of Dr. Barton, the Governor of the Asylum, I have had free access to the specimens preserved of the various strata passed through, and very careful use of them has been made in the preparation of the tabulated statement which follows; much of the information having been kindly furnished from the engineers who were employed. The Asylum is situated at Knap Hill, about a mile and a quarter from Brookwood Station on the South-Western Eailway, and is on the Upper Bagshot Sands. The mouth of the well is in the valley just below, about 140 feet above O. D., and about the same level as that at which the Middle Bagshot Beds occur in the famous Goldsworthy section, which furnished Prof. Prestwich, some forty years ago, with the clue to the succession of the beds of the Bagshot Formation. It is about a mile and a half distant therefrom. The evidence as to the horizon in the Bagshot Series, at which the well commences, is very clear to those who are familiar with the stratigraphy. The widely-extended pebble-bed at the base of the Upper Bagshot Sands occurs here very near the top of the well, and I saw it exposed again at about the same level in an excavation made by the side of the high road which runs along the western side of the Asylum Estate. The same greenish loamy sand was intermingled with the pebbles in both cases. In the ploughed field a stiff yellow loam, such as so commonly occurs above this pebble-bed in the Bagshot area, crops out in the valley where the well is situated. The ‘brown sandy bed’ which occurs at the top of the section is probably a portion of this, re-constructed by later drift action, and mingled with more sandy materials washed down from the sandy strata situated at higher levels on the slopes of the valley.