Geological Features of the District of Suchan. 45 



nodular masses of flint are very irregular in form, and variable in mag- 

 nitude; some of them scarcely exceeding the size of a bullet, while others 

 are several feet in circumference. Although thickly distributed in 

 horizontal beds or layers, they are never iu contact with each other, but 

 every nodule is completely surrounded by the chalk. Their external 

 surface is composed of a white opaque crust, consisting of an intermixture 

 of chalk and silex, probably formed by a combination of the outer surface 

 of the nodule with its investing matrix, while the former was in a soft 

 state. Internally they are of various shades of gray, inclining to black, 

 and often contain cavities lined with chalcedony, and crystallized quartz." 

 By the analysis of Klaproth flint, consists of 



Silex, 98. 



Lime, ....... '05 



Alumina, ....... '25 



Oxide of Iron, ...... "25 



Water, 1- * 



It is infusible. Submitted to a great heat it becomes white and opaque. 

 In withering it assumes various colours ; becoming most frequently 

 either red or yellow. 



It seems established by minute and extended observation, that each 

 flint is formed round some organic nucleus. Apparently these were in 

 all cases at first sponges ; and the presence of plates and spines of echini 

 shells, &c., is accounted for by supposing that the sponges grew through 

 and over such.f The silex must have been held in solution in the waters 

 from which the chalk was deposited. I believe no chemical solvent of 

 silex, has yet been discovered. It is stated, however, that steam at a 

 very high temperature dissolves it : the temperature required being a little 

 above that of fused cast iron.j We know that it is held in solution by 

 many thermal springs, especially in the Geysers of Iceland, || and in 

 thermal springs in the neighbourhood of the volcanic mountain of Ton- 

 gariro, New Zealand. § 



Dr. Buckland's theory, as published in the fourth volume of the 

 Geological Transactions, is simply this, — he assumed that the whole 

 mass was, previous to consolidation, a pulpy fluid, and that the organic 

 bodies found in the flints, were lodged in it before the separation of its 

 calcareous from its siliceous ingredients: that then these organic bodies 

 became nuclei, to which the flint, upon the principle of chemical afiSnity, 

 attached itself. ^ 



Mr. Bowerbank has examined, with great care, the flints of the upper 

 chalk, and he has arrived at the conclusion, that in all eases the siliceous 

 matter has formed itself on organic bodies ; and that these organic bodies 



♦ Mant. Gcol. Sur. of S. E. of Eng. p. 74. t Ansted, I. p. 474. 



X Rep. Brit. Ab. 1840. Jeffrey's Exp. || Hooker's Trav. 



§ Diefflnbacli. 1[ Mantell, Geol. Sur. of S. E. of Eng. 77, 78. 



