Mr. Warburton on the Bas^shot Sand. 49 



'& 



of Farnliam, it attains its greatest elevation ; there approaching within less 

 than a mile of the ridge of chalk that forms the southern limit of the London 

 Basin. The western boundary of the sand may be traced from Beacon Hill 

 Camp in a northerly direction^ rapidly declining in height^ and extending over 

 a low moorish country to Hartford Bridge : it then again acquires considerable 

 thickness,, and forms a regular escarpment extending to Broms Hill Common. 

 There its northern boundary commences, passing thence to the south of Oak- 

 ingham, at no great distance from the forest road to Reading, until it reaches 

 the hill above Egham. A line of sandy hillocks parallel to the valley of the 

 Thames marks the further progress of its northern and north-eastern boun- 

 dary at some little distance from the river by St. Anne's Hill and Oatlands to 

 the eastern extremity of the sand at Esher. 



In tracing this outline I have not entered into any very minute topographical 

 details, because the surface over which the sand extends has been laid down 

 from the observations which I made upon it^ in company with Mr. Buckland 

 and Mr, Greenough, in Mr. G.'s Geological Map of England. 



The general character of the district, in which the sand prevails, is so well 

 known as scarcely to require description. At its eastern extremity it forms a 

 chain of detached hillocks, and in its central part a high continuous plain, which 

 are strongly contrasted by their barrenness with the fertile country that sur- 

 rounds them. Such indeed is the character of the vegetation and the general 

 appearance of sterility in the worst parts of this district, that^ when the neigh- 

 bouring fertile country is hidden from the view, one may suppose one's self 

 upon a desolate mountain moor in the border country. Common hng is the 

 natural growth of the meagre sand that forms the higher parts of this district. 

 In the lower parts however, in which some argillaceous beds intervene between 

 those of sand, the vegetation is of better quality ; and the lowest parts of all, 

 which consist of a sandy loam resting upon clay, are often (as upon the skirts 

 of Windsor Forest) highly favourable to the growth of large timber. 



With regard to the position of the sand, the hill above Egham affords un- 

 equivocal proof that there at least it lies immediately upon the surface of the 

 London clay. In the clay -pits to the south of the great western road, near the 

 foot of the hill, the clay is seen characterized by its blue colour, by many of 

 the most common of its fossil shells, and by its septaria. The sand rests 

 immediately upon the clay, increases in thickness as the hill rises in height, 

 and is continuous with the great body of the sand that extends from Egham 

 Hill to the westward. 



That the position of the sand observed at Egham Hill agrees with its posi- 

 tion generally throughout the district which it occupies, cannot be doubted, 



VOL. VI. H 



