374 CRUSHED LIME-STONES. EFFECTS OF MARLS. 



The application of such mixtures must not only improve the physi- 

 cal characters of the soil, but the presence of the fragments of granite, 

 containing undecomposed felspar and mica (Lee. XII., § 1), must con- 

 tribute materially to aid the fertilizing action of the lime-stone with 

 which they are mixed. 



5°. Crushed Lime-stone. — The good effects of calcareous marls^and 

 of lime-stone gravels naturally suggest the crushing of lime-stones^as a 

 means of obtaining carbonate of lime in so minute a state of division 

 that it may be usefully applied to the soil. Lord Karnes was, I be- 

 lieve, the first who in this country endeavoured to bring this suggestion 

 into practical operation. He is said to have caused machinery to 

 be erected for the purpose in one of the remotest districts of Scotland, 

 but from some cause the plan seems never to have obtained a proper 

 trial. 



One of the results which, as we have already seen, follows from the 

 burning of rich lime is this, that it naturally falls to a very fine powder 

 as it slakes. Where coal or other combustible is cheap, therefore, it 

 may possibly be reduced to a fine powder by burning, at a less cost 

 than it could be crushed. 



Yet there are two cases or conditions in which crushing might be re- 

 sorted to with equal advantage and economy : 



FirsU where coal is dear or remote, while lime-stones and water 

 power are abundant. There are many inland districts in each of the 

 three kingdoms where these conditions exist, and in which, therefore, 

 the erection of cheap machinery might afford the means of greatly fer- 

 tilizing the land ; and. 



Second, there are in many localities rocks rich in calcareous mat- 

 ter, which are nevertheless so impure, or contain so much other earthy 

 matter, that they cannot be burned into lime. Yet, if crushed, these 

 same masses of rock would form a valuable dressing for the land. 

 Many lime-stones of this impure character, which are really useless for 

 building purposes — which do not fall to powder when burned, and 

 which have, therefore, been hitherto neglected as useless — might, by 

 crushing, be made extensively available for agricultural purposes. The 

 siliceous lime-stones (corn-stones) of the old red sand-stone, the earthy 

 beds of the mountain lime-stone, and many of the calcareous strata of 

 the Silurian system might thus be made to improve more extensively 

 the localities in which they are severally met with. The richer limes 

 now brought from a great distance, and at much expense — as on the 

 Scottish borders — might be in a great measure superseded by the native 

 produce of the district. 



§ 6. Effects of marl and of the coral, shelly and lime-stone sands, 

 upon the soil. 



The effects which result from the application of the above natural 

 forms of carbonate of lime are of two kinds. 



1°. Their physical effect in altering the natural texture of the soils to 

 which they are added. This effect will necessarily vary with the na- 

 ture of the earthy matter associated with the lime. Thus the clay 

 marls will improve, by stiffening, such soils as are light and sandy — 

 the shell sands and lime-stone gravels, by opening and rendering more 



