As a last illustration of the practice of marling we may refer to the use of chalk, which, though in some cases it must act chiefly by the lime which it contains, as when brought by railway out of Hampshire and applied at a cost of 48. per ton, on the light lands of Surrey, is nevertheless used in large quantities where it can hardly be supposed that its usefulness depends upon its lime ; as for instance on the chalk welds of Lincolnshire, of Dorsetshire, and of Hampshire, where a dressing of 80 or of 100 cubic yards of chalk at a coat of less than 3/. per acre is spread upon the land : this with boning and feeding off with sheep being the means on which the farmer depends for fertility. The boning and sheep feeding are in constant operation ; chalking is done at considerable Intervals of time. One chalk is found to be much bette,than another for use in this way ; differences which seem to indicate that their fertilising influence is not owing merely to their lime, but to some other ingredients--probably phosphate of lime, which is found in some chalk marls in considerable quantity. Thus,
thanks to the researches of Messrs. Paine and Way into the chemical and agricultural character of the chalk formation, we have learned the existence of marl, containing very considerable proportions of phos phoric acid combined with lime, to which undoubtedly, and not to the carbonate of lime which it also contains, its fertilising influence is due. We may also mention as an illustration of the way in which the farmer may be misled by terms, that in this same district a bed of white earth is quarried and used upon the sandy lands of the locality with the best effect, which is called a marl, although hardly a trace of lime exists in it ; the effect being no doubt due to the largo proportion of the soluble silica which it is found to contain. It may be noticed that the shelly sand of the shore is largely used in Cornwall and on some parts of the Irish coast, and carried many miles inland, with the best effect on the fertility of the limeless soils to which it is applied.