d 



parts of the same noJale. Though any analysis, therefore, can only apply 

 strictly to the particular sperimcn examined, cither as regards the amount of 

 lime or the degree or kind of impurity, yet the foUowing analyses give a fair 

 idea of the composition of the less impure varieties. Sir Henry De la Beche 

 (Mem. Geo, Survey) gives the following analysis of a Cornstone nodule :— 



Carbonate of lime 69^3 



Peroxide of iron 2"2 



Silica 19;5 



Alumina 7"2 



Water 0"9 



Traces of chlorides, sulphates, and loss 9 



100.0 

 A specimen of burned lime from the quarry near Ford Bridge station was 

 examined for Mr. Arkwright, by Dr. Voelcker, with the following result :— 



Water of combination.... 9 35 



Oxides of iron and alumina 6'06 



Lime 52.42 



Magnesia I'lo 



Alkalies 0-24 



Carbonic acid 11.43 



Insoluble sUiceous matter 18 77 



100-00 

 Nearly three fourths of the carbonic acid had been expelled by burning. Tho 

 quantity of lime is equivalent to about 72 per cent, of carbonate of lime. Mr. 

 Arkwright has kindly placed in my hands three other analyses from different 

 quarries on the Hampton Court Estate. In these the quantity of carbonate 

 was found to be— the Sheepstye quarry, 60 ; Egdon Hill, 67 ; and Foxalls quarry 

 69 per cent. 



In these thirteen specimens, which I now show you, from different beds 

 and from different parts of the country, and which you will see differ greatly 

 in character, I have found the proportion of carbonate of lime varying from 

 38 to 88 per cent. 



In all the forms I think the lime was deposited from a chemical solution, 

 aided in the conglomerate varieties by mechanical action, and not as in some 

 formations by animal life. In the two classes, however, I believe the mode of 

 deposition was very different. The great beds of concretionary limestone in this 

 neighbourhood do not present any stratification or such irregularities in tho 

 different portions of the beds as currents would be likely to produce. Tho 

 mineral matter mixed with the lime is in the form of an exceedingly fine mud, 

 such as would be held in suspension for some time, and slowly deposited in still 

 water. I think we may infer therefore that they were deposited as a limy mud 

 in a still sea bottom, the nodules being formed subsequently by a process of 

 crystallization, by which the carbonate of lime became aggregated in masses prior 

 to the consolidation of the deposit. The smaller bands, or rows of nodules, found 

 imbedded in marl, may be explained in the same way, sand and clay containing a 



