Rev. A. Irving — The Brookwood Well-Section. 353 



means of designating rocks of this kind, and as this appears to be the 

 only variety of diorite which is found in the boss at Brazil Wood, 

 it might be termed the Brazil Wood type of diorite. If we do this, 

 we may then state that diorites of the Brazil Wood type occur in 

 Warwickshire associated with Cambrian strata, and also in Anglesea, 

 the Lleyn Peninsula, and the Lake District. It is worthy of note 

 that in no single instance is a diorite of this type known to be 

 associated with Upper Palasozoic or later strata in Britain. I have 

 a specimen of diorite from Glen Tilt (Perthshire) of the same general 

 type, but can say nothing about its mode of occurrence. 



The differences between diorites of the Brazil Wood type and 

 those from Inchnadampf described in the present paper have already 

 been referred to. The interesting fact of the close relation of these 

 diorites to Prof. Bonney's hornblende-picrites has also been pointed 

 out. 



V. — The Brookwood Deep- Well Section. 

 By the Eev. A. Irving, B.Sc, B.A., F.G.S. 



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 Bail way, and is on the 

 Upper Bagshot Sands. The mouth of the well is in the valley just 

 below, about 140 feet above 0. D., and about the same level as that 

 at which the Middle Bagshot Beds occur in the famous Golds worthy 

 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, 1 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 



1 Vide Q.J.G.S. for August, 1885, pp. 493 (No. 2 of the Section). 



DECADE III. VOL. III. — NO. VIII. 23 



