USE OF LIME-STONE SAND AND GRAVEL. 373 



cause it contains both more saline and more animal matter. This ani- 

 mal matter enables it to unite in some measure the beneficial effects 

 which follow from the application of marl and of a small dressing of 

 farm-yard or other valuable mixed manure. 



Payen and Boussingault ascribe the principal efficacy of the shell 

 and coral sands to the small quantity of animal matter which is present 

 in them. These chemists estimate the relative manuring powers of 

 different substances applied to the land by the quantities of nitrogen 

 which they severally contain, and thus, compared with farm-yard 

 manure, attribute to the shell and coral sands the following relative 

 values: — 



Contain of Relative 



Nitrogen. value. 



100 lbs. of Farm-yard Manure . . . 0-40 lbs. 100 



do. of Coral Sand (Merl) . . . 0-512 lbs. 128 



do. of Shell Sand (Trez) . . . 0-13 lbs. 32^* 



That is to say, that, in so far as the action of these substances is de- 

 pendent upon the nitrogen they contain, fresh coral sand is nearly one- 

 third more valuable than farm-yard manure, while fresh shell sand is 

 only equal in virtue to one-third of its weight of the same substance. 



Though, as I have already had frequent occasion to observe to you, 

 much weight is not to be attached to such methods of estimating the re- 

 lative values of manuring substances by the proportions of any one of 

 the ingredients they hajipen to contain — yet the fact, that so much ani- 

 mal matter is occasionally present in the living corals, accounts in a 

 satisfactory manner for the immediale effects of this form of calcareous 

 application. This animal matter acts directly and during the first year; 

 the carbonate of lime begins to show its beneficial influence most dis- 

 tinctly when two or three years have passed. 



4°. Lime-stone Sand and Gravel. — In coimtries which abound in 

 lime-stones, there are found scattered here and there, in the hollows and 

 on the hill-sides, banks and heaps of sand and gravel, in which rounded 

 particles of lime-stone abound. These are distinguished by the names 

 of lime-stone sand and gravel, and are derived from the decay or wear- 

 ing down of the lime-stone and other rocks by the action of water. 

 Such accumulations are frequent in Ireland. They are indeed exten- 

 sively diffused over the surface of that island, as we might expect in a 

 country abounding so much in rocks of mountain lime-stone. In the 

 neighbourhood of peat bogs these sands and gravels are a real blessing. 

 They are a ready, most useful, and largely employed means of im- 

 provement, producing, upon arable land, the ordinary effects of liming, 

 and, when spread upon boggy soils, alone enabling it to grow sweet 

 herbage and to afford a nourishing pasture. The proportion of carbon- 

 ate of lime these sands and gravels contain is very variable. I have 

 examined two varieties from Kilfinaue, in the county of Cork (?). The 

 one, a yellow sand, contained 26 per cent, of carbonate of lime — the re- 

 sidue, being a fine red sand, chiefly siliceous ; the other, a fine gravel 

 of a grey colour, contained 40 per cent, of carbonate of lime in the 

 form chiefly of rounded fragments of blue lime-stone, the residue con- 

 sisting of fragments of sand-stone, of quartz, and of granite. 



• Annalee de Chim. st de Phys.^ third series, iii., p. 103. 



