ON THE USE OF LIME, MARL, AND SHELL-SAND. 



25 



nodules, which in appearance can hardly be distinguished from 

 ordinary chalk marls, is indicative of good soils. In localities on 

 the greensand or lower chalk formation, farmers should have a 

 special look-out for phosphatic nodules, inasmuch as their notice 

 may probably lead to the discovery of Coprolite beds. Unfortu- 

 nately many phosphatic nodules cannot be distinguished by their 

 physical characters from common chalk marl, and the tests for 

 phosphate of lime are too complicated to enable any one not 

 well acquainted with analytical chemistry to detect with pre- 

 cision the presence of phosphoric acid. 



4. Shell or sea sand. Shell-sand is calcareous sand which 

 consists of the fragments of broken shells, corals, silicious sands, 

 debris of granite, and small quantities of animal matter and 

 soluble alkaline salts. It differs much in colour and fineness, 

 &c., as well as in chemical composition, and consequently also in 

 quality. Extensive deposits of shell-sand are found in many 

 parts of the Devonshire and Cornish coasts, for instance at Bude, 

 Barracaine, Northcote Mouth, Hartland Quay, and especially at 

 Padstow. There is an immense deposit of indefinite depth in 

 the estuary of Padstow, from whence it is transported in large 

 quantities to great distances inland. It has been estimated that 

 4,000,000 of cubic feet are annually employed for agricultural 

 purposes in Cornwall alone, in which county shell-sand is held in 

 high estimation, since it is peculiarly well adapted as a manure 

 for the soils of Cornwall. These soils are generally either stiff 

 clays or poor sands ; they result chiefly from the disintegration of 

 the granitic and schistose rocks that abound in Cornwall, and are 

 very deficient in lime ; hence the utility of shell-sand, which 

 owes its fertilizing qualities principally to the carbonate of lime 

 which it contains. 



Most of the samples of Cornish and Devonshire shell-sand 

 which I examined were supplied to me by my friend and pupil 

 Mr. E. Hockin, of Bude, who also kindly made several shell- 

 sand analyses for me. The results of Mr. Hockin's analytical 

 examinations are embodied in the subjoined tabular statement : 



Composition of Sea-sand (Shell-sand') from Devon and Cornwall. 



