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



According to these results, good chalk contains from 95 to 98 

 per cent, of pure carbonate of lime ; but neither the samples of 

 the lower chalk nor the upper chalk beds which were analysed 

 contained much phosphoric acid. I cannot help thinking that 

 money is often spent uselessly in the chalk districts in sinking 

 pits and bringing to the surface-soil a variety of chalk which 

 may be harder or somewhat different in colour, but otherwise 

 does not materially differ from the chalk of the upper beds. It 

 is true, phosphate of lime is more abundant in the beds of the 

 lower chalk than in those of the upper chalk, but it is also true 

 that there are beds as poor in phosphates in the lower as those 

 in the upper chalk. Unless, therefore, a bed considerably richer 

 in phosphates is reached in sinking a chalk-pit, labour and 

 money are likely to be thrown away. The analysis of the chalk 

 which it is intended to bring to the surface, with especial refer- 

 ence to the phosphoric acid contained in it, at once would decide 

 the question whether it is desirable to go to the expense of 

 sinking a deep chalk-pit "or not. 



3. Marl. A third form in which lime is applied to the land 

 is that of marl. The term marl is used often in rather a loose 

 sense, and applied sometimes indiscriminately to all mineral 

 matters which are dug up and put on the land in large quantities. 

 Hence, mineral manures possessing properties widely differing 

 from each other pass by the name of marl ; and agricultural 

 writers have to distinguish a great variety of marls : such as 

 clay marls, shell marl, sandy marl, chalk marl, peaty marls, stony 

 marls, dry and wet marls. 



I shall not attempt to describe here the properties and appli- 

 cation of the different kinds of marls which are used in agricul- 

 ture, but shall confine myself to a brief account of a few marls 

 which are used in the West of England, and which I had an 

 opportunity of examining. I am aware that there are many 

 marls used for manuring purposes in Devonshire and Somerset- 

 shire, as well as in Cornwall and South Wales, which I have not 

 examined. Numerous applications for marls used for agricul- 

 tural purposes were met with no response, and I had consequently 

 no opportunity to analyse several kinds of marls which I should 

 have liked to examine. However, to confess the truth, I am 

 almost glad that I have not to report on the agricultural value of 

 many specimens of marls, for I am afraid I could not have done 

 justice to the subject in the limited time allowed to me for exa- 

 mining into the various calcareous manures that are found in 

 the West of England, and for reporting on their uses in agri- 

 culture. 



" The Marls of the West of England, and their uses in agri- 

 culture," is a subject quite comprehensive enough by itself, and, 



