ON THE USE OF LIME, MARL, AND SHELL-SAND. 11 



Mr. Watson, of Dorsley, who kindly forwarded to me these 

 three limestones occurring in the neighbourhood of Totnes, 

 informs me that Dartbridge Quarry is ^situated 8 miles from 

 Petehole Quarry and 12 miles from Habertonford Quarry, and 

 Petehole Quarry is situated 4 miles from Habertonford Quarry. 



Like the Habertonford limestones, that from Petehole Quarry 

 contains a large quantity of insoluble silicious matter and sand. 

 The lime which enters into its composition does not all occur as 

 carbonate, but some of it is in combination with sulphuric acid, 

 as well as with silicic acid. The proportion of sulphate of lime 

 in this limestone is much larger than usual. It also contains 

 organic matter, in the shape of graphite, a constituent which 

 rarely enters into the composition of limestones. This stone 

 appears to be a limestone changed from its original constitution 

 by subsequent volcanic action and admixture of the products of 

 violent subterranean commotion. 



I have not learned whether or not the Petehole limestone 

 makes good lime, but am inclined to think that it will not. At 

 any rate, it is evident that this stone, which contains only 71 

 per cent, of carbonate of lime, cannot produce a lime as valuable 

 for agricultural purposes as the limestone from Dartbridge 

 Quarry, in which stone no less than 95 per cent, of carbonate of 

 lime occurs. 



In the next Table I have arranged the results of two speci- 

 mens of Lias limestone from Aberthaw, Glamorganshire. 



Composition of Lias Limestones from Aberthaw, Glamorganshire. 



1st Specimen. 2nd Specimen. 



Moisture ., '260\ 



Water of combination . . 

 Oxides of iron and alumina 

 Phosphoric acid 

 Carbonate of lime 

 Sulphate of lime 

 Carbonate of magnesia . . 

 Insoluble silicious matter 



290J 

 483\ 

 167 / 



666 

 1-333 



89-870 .. .. 89-332 

 110 not determined. 



880 .. .. 2-336 



8-120 .. .. 6-333 



103-180 100-00 



Both analyses were made with stones from the same quarry. 

 It will be seen that No. 2 contains more magnesia and less 

 insoluble silicious matter than No. 1, and that both contain 

 about the same quantity of carbonate of lime. The quicklime 

 obtained from it is rich in lime, but, like most Lias limes, it 

 does not swell much on slaking, and is better adapted for 

 cement-making than for quicklime. Still, in the absence of a 

 better lime, it is usefully employed for agricultural purposes. 

 Lias lime, when used for agricultural purposes, I may observe, 



