138 



Dr. FiTTON on the Strata below the Chalk* 



7. Bottom of the quarry. Stone unfit for working, from its containing much flinty 



matter. 

 All these strata dip at a very small angle to about 20" west of south. The rock is traversed 



by fissures, which divide it into somewhat rhomboidal masses ; and smaller cracks are 



sometimes found within the blocks of stone. 



(47.) The gault hereabouts occupies a tract which bears the name of 'Black- 

 land/' and forms a slight depression below the band which affords the firestone. 



(48.) The lower green-sand has distinct indications of a subdivision into 

 threCj like that of the vicinity of Polkstone (16.). On the line of section, 

 No. 2. Plates VII. and X. ponds are frequent^ in a situation corresponding 

 to that of the greener middle group (24.) ; the surface being comparatively 

 low, with vegetation of a somewhat different character. The stony beds of 

 the lowest group then rise to form the escarpment of Tilburstow Hill*, which 

 is nearly on a level with the chalk downs ; and at the highest point, there is 

 decisive evidence either of a sinking towards the chalk, or of elevation in an 

 op])osite direction ; for at the top of the hill, the beds, which on the north of 

 that place rise uniformly at an angle of not more than 10°, are suddenly 

 thrown up to about 45°. The appearance of the section here is represented 

 in the sketch subjoined : 



Norl 



and furnaces, but is employed also for buildings under water. Great care is necessary, in build- 

 ing, to place the blocks so that the planes of stratification shall be horizontal. The equivalent of 

 these beds in the upper green-sand of the continent, (the Planer kalkslein of the Germans,) is 

 employed for exactly the same purposes, at Aix-la-Chapelle and other places. 



* This is the spelling of the Ordnance map : the word in the country is pronounced " Tilbuster." 



