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



Habertonford quarry, situated just at the end of the trap-rock 

 district. When used for building walls it forms a mass as hard 

 as rock, and it sets as a cement when used for forming ponds, 

 for which purpose it is largely employed. 



Composition of Hydraulic Limestone from Habertonford Quarry, 

 near Totnes. 



Water of combination 



Oxides of iron and alumina 



Carbonate of lime 



Sulphate of lime 



Magnesia (in the state of silicate) 

 Insoluble silicious matter (clay and sand) . . 

 Alkalies (in the state of silicates) 



100-00 



A much inferior cement, or, properly speaking, a bad lime, is 

 produced on burning a lias -limestone which occurs at Stapleton, 

 near Bristol. A specimen of this stone gave, on analysis, the 

 following results : 



Water of combination, and a little moisture 



Oxides of iron and alumina 



Carbonate of lime 



magnesia 



Insoluble silicious matter (clay and sand) .. 



100-00 



Other lias limestone from the West of England will be de- 

 scribed presently under agricultural limestones. 



To give an example of a silurian limestone, which partakes of 

 the characters of a hydraulic lime after burning, the following 

 analysis, to which I submitted a limestone from Pembrokeshire, 

 may be stated : 



Composition of Silurian Limestone from Clynderwen, Pembrokeshire. 



Moisture, driven off at 212 Fahr. .. .. -18 



Water of combination *52 



Oxides of iron and alumina '91 



Containing phosphoric acid * (-022) 



Carbonate of lime .. _ 81-70 



Sulphate of lime -10 



Carbonate of magnesia '79 



Insoluble silicious matter 15-86 



100-06 



It will be seen that all three limestones are very impure, but 

 although the amount of carbonate of lime is larger in the Haber- 

 tonford lime than in the two others, it produces a better cement, 



