Dr. FiTTON on the Strata below the Chalk. 109 



green matter is of the same nature. A slight examination of the green par- 

 ticles, which Sir John Herschel had previously the goodness to make for me, 

 intimated the same results. 



(11.) Gault. The rise of this stratum on the shore is also obscured by ruins 

 of the superior beds; but it is visible in detached points, at low water, in 

 Eastware Bay, and forms the greater part of the cliff at Copt Point, where 

 many of the more beautiful specimens of the Gault fossils, seen in collections, 

 have been obtained. It appears also below the outlier of the upper green- 

 sand already mentioned (Plate X a. No. 1.); and occupies nearly the whole 

 of the grassy and ruinous cliff between the base of the Martello Tower No. 2, 

 and the sea. Its total thickness is about 130 feet, and it may be divided into 



even by the nitro-muriatic. It gives out water when heated, and becomes brown from its iron 

 passing into the state of peroxide. As it has been supposed to owe its green colour to the pre- 

 sence of phosphoric acid, it was carefully examined, with the view of detecting that acid, if present. 

 It was accordingly fused with carbonate of soda, the alkaline filtered solution neutralized by nitric 

 acid, and evaporated to dryness, and the neutral solution tested by nitrate of silver and nitrate of 

 lead. Of two samples of green-sand, thus examined, one was found to be quite free from phosphoric 

 acid, and traces only were detected in the other. The former was also free from lime, and the latter 

 contained but a small portion. It is hence obvious, that neither lime nor phosphoric acid are 

 essential constituents of the colouring matter of green-sand, and their presence must be regarded as 

 casual. 



" In order to determine the chemical constitution of the colouring matter, I collected some green 

 particles from the calcareous sand of Eastware-bay, near Folkstone, removing all foreign matter 

 as far as possible, by washing with water and dilute acid. The only impurity which I could detect 

 after this treatment consisted of small grains of quartz, the quantity of which varied in different 

 samples. 



"A portion of green particles thus purified, very free from oxidation, and dried at 212° Fahr. 

 lost 7'0 per cent, of water when heated to redness. 



"Another portion of the same sample was fused with carbonate of soda, and the earthy ingredients 

 subsequently separated and weighed in the manner usual in such analyses, 



" A third portion was heated with carbonate of baryta, and examined for potash, traces of which 

 were readily found. According to the total result, the green particles consist of 



" Silica 48-5 



Black Oxide of Iron 22*0 



Alumina 17'0 



Magnesia 3'8 



Water 7-0 



Potash traces 



♦'98-3 



[M. Berthier's analysis of the green particles from 

 near Havre gave the following proportions : — 



Silica 50-0 



Protoxide of Iron 2 TO 



Alumina 7*0 



Water 11-0 



Potash 10-0 



99-0.] 



"It is superfluous to speculate on the precise atomic constitution of the green particles, since they 

 were not obtained in a state of perfect purity. The ingredients which appear to be essential, 



