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



IV. contains more than sufficient oflime to answer all the require- 

 ments of the crops of a rotation, and the further addition of fresh 

 lime therefore could not do any good (so far as the supply of 

 constituents of plants is concerned). Indeed it may be questioned 

 whether the repeated liberal doses of lime have not hastened the 

 exhaustion of this soil in grain-producing constituents. This 

 circumstance led me to determine the quantity of phosphoric 

 acid, which I found to amount in this soil to only "147 per 

 cent. 



There can thus be no doubt but that superphosphate and other 

 phosphate manures will much improve this and similar soils, and 

 I cannot help thinking that there are many soils in Devonshire, 

 Somersetshire, Cornwall, and South Wales, upon which a portion 

 of the money now spent in the purchase of lime or shell-sand 

 might be much more economically laid out in the purchase of 

 artificial manures, especially those rich in phosphates ; or in the 

 purchase of oil-cake, the consumption of which on the farm 

 would tend to produce a much more valuable manure than is 

 found at present on many farms, especially in Wales and some 

 parts of Devonshire. 



The rocks on which Mr. Watson's soils rest have also been 

 analysed by me, and as their composition may be of some 

 interest, I subjoin a Table which contains the results of analyses 

 of three rocks from Dorsely. 



No. I. is a specimen of the rock immediately under the soil. 

 It is a brown-coloured rock. 



No. II. is a specimen of the rock subjacent to No. I. Colour 

 of rock bluish-grey, occurring at a depth of from 2 to 6 feet. 



No. III. shows the intermixture of No. I. and II. 



No. I. No. II. 



Brown Rock. Blue Rock. 



Water of combination .. 6*274 .. 4'360 



( )xidcs of iron and alumina 



Phosphoric acid 



Carbonate of lime 



Magnesia 



Insoluble silicious matter . . 



27-854 .. 26'452 



250 .. -508 .. 



1-234 .. 10-040 : ..' 7i 



3-008 .. *2-008 .,--; 



61-274 .. 56-580 4.4 



100-538 100-000 100-00 



Comparing these results with each other, it will be observed 

 that the brown rock contains very little lime, and just half the 

 amount of phosphoric acid which is contained in the blue rock 

 on which the brown rock rests, whilst there is no less than 10 

 per cent, of carbonate of lime in No. II. The rock No. III. 

 contains 8 per cent, of lime and less phosphoric acid than No. 



* Determined by loss. 



