120 GEOLOGY. 



ON THE PLEISTOCENE TUFACEOUS DEPOSIT, AT 

 BLASHENWELL. 



[ Eead at St. Aldhelm's Head, July 2nd, 1857. ] 



A traveller passing through the Isle of Purbeck, must be 

 struck Avith the variety of its agricultural features: rich pas- 

 tui-ages, and wall-bound fields, with soil so shallow as to render 

 their cultivation scarcely profitable, is the general character of 

 the district. This succession is interrupted in a field adjoining 

 Corfe Common, where a bed of flint gravel, over-lying the 

 Hasting's sands, interferes with the usual fertihty of that deposit. 

 When the district is more carefully examined, and science ap- 

 plied to develope its capabilities, much that is supposed to 

 be profitless may be turned to some account, either for agri- 

 cultural or manufacturing purposes. These remarks are 

 applicable to a spot near the village of Kingston, whose rich 

 calcareous substratum may not only be made useful as an 

 auxiliary for imparting luxuriance to its less fertile neighbours, 

 but, by the aid of this key, other localities possessing similar 

 beds, may be employed for the same good ofifice. 



At Blashenwell, the clays which intersperse the Purbeck beds, 

 form an impenetrable barrier to the drainage of the hill, forcing 

 the water to the surface through the disturbed strata of these 

 beds. I conceive this spring in bye-gone days, had much to do 

 with the formation of a tufaceous bed near the farm house, and 

 which probably extends over a considerable area. 



My attention was attracted by the white appearance of the sub- 

 soil through which a road was cut for the convenience of the 

 farm. Upon examination, I found it consisted of four distinct 



