380 PROCEEDINGS OE THE GEOLOGICAL SOCIETY. [May 26, 



Farnliam on the south to Wokingham on the north*. They also 

 form numerous outhers both to the westward and eastward of this 

 main mass, appearing on the summits of Harrow, Hampstead and 

 Highgate hills ; and I have further traced them on some of the hills 

 near Epping, at Havering-atte-Bower, Brentwood, Langdon, and as 

 far as the hills around Rayleigh, near Southend. 



These sands are everywhere in distinct and conformable superpo- 

 sition to the London clay, but nowhere, that I have yet seen, is there 

 any other deposit incumbent upon them. 



A wanderer amongst formations, without determined age or super- 

 position — by some considered the equivalent of our most recent tertiary 

 series, the Crag^, — by others referred to the sands superimposed upon 

 the Freshwater strata of Hampshire^ ; frequently placed rather lower 

 than this §, and (as its lowest assigned position) sometimes grouped 

 with the sands overlying the Barton clays at Alum Bay, and forming 

 the base of Headon Hill (see PI. XIV. Gen. Sec. fig. 2, No. 30) : on the 

 continent sometimes placed in co-relation with the Gres de Fontaine- 

 bleau II, but more usually with the Gres de Beauchamp ^, — the de- 

 posit known as the Bag shot sands still presents a problem in geolo- 

 gical chronology and stratigraphical structure**. 



In investigating this question I have traversed the Bagshot sands 

 in every direction, from Southend to Newbury, and yet have collected 

 but a small number of positive facts. Few however though they are, 

 they all give concurrent testimony, and being supported by a mass of 

 negative evidence, possess I think greater weight than numerically 

 they would be entitled to. 



As with the London clay in my previous paper, I do not now intend 

 to enter minutely into the details of structure, but to restrict myself 

 merely to such a general view as will suffice for a comparison with 

 the strata which I hope to prove to be their equivalents in Hampshire 

 and the Isle of Wight. 



The Bagshot sands have been described as an irregular mass of un- 

 fossiliferous siliceous sands, with occasional subordinate beds at their 

 base of fossiliferous green sands and marls. Of the relative super- 

 position and range of their component strata ; of their comparative 

 development, persistence and thickness, and of the distribution of the 

 fauna, further details are however yet required before their age and 

 structure can be well determined. To these points we will therefore 

 direct our attention. 



Notwithstanding the apparent indistinctness and irregularity of these 

 sands, their structure is far more regular and persistent than could be 

 anticipated at first sight. The sandy heaths of Woking, Ascot, Cob- 



* For further details of the range of outcrop of these sands, see Mr. Warburton's 

 paper. See also Dr. Mantell's Geology of Surrey, in Brayley's ' Surrey,' and Cony- 

 beare's and PhilHps's Geology. f Bakewell's * Introduction to Geology.' 



X Warburton's paper before quoted ; and in most Geological maps. 



§ In Conybeare's and Phillips's Geology of England it is placed as the Upper 

 Marine Formation, an arrangement since very generally followed. 



II Brongniart's * Tableau des Terrains.' 



% D'Archiac, Bulletin de la Soc. Geol. de France, vol. x. p. 200. 



** See note, ante, p. 359. 



