By the Ven. Archdeacon MacdonaJd. 155 



tinguished from the Upper Green Sand, that it will not be necessary- 

 further to define its limits. It has in the neighbourhood of Devizes 

 a depth of about 500 feet, probably a little more. Roundway Hill 

 is 740 feet above the sea ; Morgan's Hill 940. On the summits of 

 some of the hills, there are beds of the Upper Chalk, with layers 

 and nodules of flint. Here the Chalk is very pure and soft ; at a 

 lower level there are layers of a hard splintery limestone, occasion- 

 ally of a yellowish tinge, and towards the base of the stratum it 

 becomes more argillaceous, and of a grey tint; sometimes when 

 wet, it approaches to a slate colour. The general appearance of 

 the Chalk however is that of a soft whitish limestone : chemically 

 speaking, it is carbonate of lime. In some localities, it is much af- 

 fected by the weather, and breaks up into thin scales, whilst in other 

 instances it is sufficiently hard and enduring to serve as a material 

 for building rough walls. 



Phosphate of lime, the most valuable of all inorganic manures, 

 abounds in the hard beds of the Lower Chalk. The pieces in which it 

 occurs may be known by their yellowish tinge and irregular nodular 

 structure. The stone containing it is much used in the town and 

 neighbourhood of Devizes as a material for road making : some of it 

 contains as much as 25 per cent, of phosphate of lime. In its passage 

 into the Upper Green Sand, the Chalk gradually becomes mixed with 

 coarse silicious sand, and the great abundance of organic remains, 

 would lead to the conclusion that these particular beds were depos- 

 ited at the bottom of a shallow sea, abounding with vegetable as well 

 as animal life. The fossils here found mostly constitute the nuclei 

 of small masses of phosphate of lime, or they are filled with that sub- 

 stance. The nodules generally contain 40 per cent, of phosphate 

 of lime. The following is the analysis of some specimens from the 

 neighbourhood of Roundway, by Dr. Wrightson of Birmingham. 

 Sand and silicates - - - 25 • -'!;; 



Carbonate of lime - - - 27 ■ 70 



Phosphate of lime - - - 12 ■ 46 



Alkalies, & - - - 4 • 5 1 



100 

 k 2 



