ANNUAL ADDRESS, MDCCCLXXIII. 41 



I will now briefly turn to the nature and composition 

 of limestones. They are all mainly composed of calcium, 

 oxygen, and carbon, or what is commonly called carbonate 

 of lime, the formula of which is CaCOs or CaOCCte, 

 that is, one molecule of oxide of calcium, which is lime, 

 united with a molecule of oxide of carbon or carbonic 

 acid ; or, an atom of calcium united chemically to an atom 

 of carbon with three atoms of oxygen ; or, to be more 

 precise in stating their respective affinities, one atom o^ 

 calcium united with one atom of oxygen forms oxide of 

 calcium or lime : this combination or molecule combines 

 with another, consisting of one atom of carbon united 

 with two atoms of oxygen or carbonic acid, and forms 

 limestone, and it is the same whether it occurs as calc- 

 spar, chalk, oolite, coral reef, Atlantic ooze, the shells of 

 molluscs, or the egg-shells of birds. 



In the case of magnesian limestone it is different : it 

 then contains upwards of 20 per cent, of carbonate of 

 magnesia. The quantity of magnesia is however variable. 

 Magnesian limestone is said to be the result of the 

 gradual metamorphosis of ordinary limestone, carbonate of 

 magnesia replacing carbonate of lime. To my own mind 

 this mode of accounting for the difference is doubtful, as 

 sea water usually contains more carbonate of magnesia in 

 solution than carbonate of lime. But limestones are all 

 more or less impure. My friend Mr. Woodcroft, who has 

 very kindly and at considerable trouble made a careful 

 examination of the mountain limestone of Caldon Low, 

 gives the following as the result of his analysis: Car- 

 bonate of lime, alumina, silica, carbonaceous matter, and 

 a trace of iron. Out of 30lbs. of limestone dissolved in 

 hydrochloric acid, the residue well washed with distilled 

 water, he found 680 grains of mud, consisting of alumina 



