CHALKS AND MARLS. 229 



draw the especial attention of my readers to the occurrence of 

 phosphate of lime, in sensible quantity, in many marls, the pre- 

 sence of which ought to render them much more valuable as 

 applications to the land. In the marls of the green sand, Mr 

 Nesbit, Mr Payne, and Mr Way, have found this phosphate to 

 exist sometimes to the amount of 14 per cent. ; and Mr Payne, 

 who is an extensive and skilful hop-grower, pronounces these 

 marls to be possessed, when applied to his land, of highly ferti- 

 lising qualities. 



The suggestion I would make on this subject, therefore, is, that 

 the existence of phosphate of lime in marl beds should be more 

 generally sought for ; and that the value of such marls, when 

 the quantity of phosphate amounts to two or three per cent, 

 should be carefully tested by experiment. Such marls, though 

 , comparatively poor in lime, may be very economical applica- 

 tions to the land, even where rich chalks and limestones are 

 readily accessible. They may promote the growth of corn, may 

 give an excellent quality of grain, may maintain the fertility of 

 the land without the use of bones, and may cause bones when 

 applied to produce a less sensible effect than they are usually 

 seen to do. 



Thus, while the discovery and use of marls of this kind may 

 prove a source of public advantage and of individual gain, 

 it will also aid the progress of scientific agriculture, by spread- 

 ing a knowledge of the principles on which the fertilising quali- 

 ties of different substances depend, and by affording a key to 

 discordant results which often perplex the farmer. 



The value of marls, the practical man will learn, is not al- 

 ways to be measured merely by the percentage of lime they 

 contain. If two marls produce different effects, the difference 

 may, in all likelihood, be traced to a difference in composition. 

 If they diminish the after-action of bones, it must be that they 

 contain ingredients which are capable of producing some of 

 the effects which usually follow from the application of this 

 manure. The ingredient they are most likely to contain is the 

 phosphate of lime. This, therefore, should be sought for, and 

 its quantity ascertained. 



