1867.] MAW TERTIAEY WHITE CLAYS. 391 



Tc. Analysis of " Blue Clay," Bovey Tracey Lignite-deposit, from the clay- 

 works of Messrs. Watts, Blake, Bearne & Co., Newton Abbot. 

 /, Analysis of "Blue Clay," Dorsetshire, Lower Bagshot. 

 m. Analysis of " Brown Clay," Dorsetshire, Lower Bagshot. 



The following are taken from the Catalogue of Eock Specimens in 

 the Museum of Practical Geology (3rd edit. p. 167) : — 



n. o. 



Silica 65-49 72-23 



Alumina 21-28 23-25 



Oxides of iron 1-26 2-54 



Alkalies and alkaline earths 7-25 1*78 



Sulphate of lime 4'72 



Loss -- 0-20 



10000 100-00 



n. Analysis of " White Pipe-clay " (Lower Bagshot), Branksea Island, Dor- 

 setshire, by Prof. Way. 



o. Analysis of " Black Clay " (Lower Bagshot), Branksea Island, Dorsetshire, 

 by Prof. Way. 



Mr. Charles D. Blake, of Newton Abbot, referring to the clays of 

 the Bovey Tracey lignite-deposit, says : — "Speaking generally; I may 

 state that our mines produce clays containing silica and alumina in 

 every proportion, between 95 per cent, of silica (maximum) down 

 to 50 per cent, of silica (minimum), and from 50 per cent, of alumina 

 (maximum), down to 4 per cent, of alumina (minimum) ; also that 

 some of our clays are nearly pure silicates of alumina, containing 

 no free siHca, whereas others contain as much as 70 per cent, of free 

 silica. 



These variations in the composition of both the white Tertiary 

 clays, as well as of the chalks, would render a comparison between 

 individual examples of little value ; but by comparing, as foUows, 

 the average composition of a number of clays, with the average 

 proportion of silica and alumina contained in the series of chalk 

 examples before described, a fair means of comparison may be 

 arrived at. 



(p) Average composition of clays i, j, h, I, m, n, and o : — 



Silica 61-01 



Alumina 32-06 



Oxide of iron 1*76 



Magnesia , 0-76 



Lime, sulphuric acid, alkalies, loss, water, &c. ... 4-41 



100-00 



Let us now see how far this composition agrees with that of the in- 

 soluble residue that would remain after the carbonate of lime and 

 other soluble constituents of the chalk have been deducted as 

 removable by water charged with carbonic acid. Nearly the whole 

 of the silica and alumina, the peroxide of iron, and part of the 

 magnesia would remain behind, and a portion of the magnesia would 

 be removed with the carbonate of lime : as the soluble and insoluble 



