Mr. J. S. Bowerbank on the Siliceous Bodies of the Chalk. 261 



and differing in tint according to the absence or presence of small 

 varying quantities of foreign matter, such as iron or manganese/^ 



It is evident from this passage that Dr. Turner had chalce- 

 dony more especially in his mind when he penned this passage, 

 and that in reality he believed flints to have originated from or- 

 ganized bodies by slow infiltration, for the last passage quoted is 

 immediately succeeded by the following one : " In the case of 

 flint it was necessary," he said, " to account for that remarkable 

 tendency which silica possessed to occupy the place of organic 

 matter, as exemplified by the specimens of flint, silicified wood, 

 and coral on the lecture- table. This phsenomenon the lecturer 

 thought might be explained on the principles which had been 

 developed that evening. Siliceous solutions infiltrating through 

 organic masses in progress of decay, might readily be decom- 

 posed by the afiinity of gases or other compounds generated 

 during slow putrefaction, either for the silica itself or for its 

 solvent. In either case a deposit of silex would result." From 

 this passage it would appear that, although he quotes the sup- 

 position of Brongniart, he was for his own part of opinion that 

 the slow infiltration and deposit through the agency of the de- 

 composition of organic bodies had been the means of the forma- 

 tion of flint. 



Let us now inquire what foundation there is for the supposi- 

 tion that flints are formed from detached masses of gelatinous 

 solution of silex. Have such solutions ever been found in na- 

 ture ? Is there a single writer on chemistry or mineralogy who 

 describes such a condition of silex as natural ? Mackenzie in 

 his account of Iceland speaks of the vast deposits of silex in the 

 form of siliceous sinter, and of its encrusting the living stems of 

 grasses, but says not a word of its ever occurring in the gelati- 

 nous form under any circumstances; and Mr. C. C. Babington, 

 who has recently returned from a visit to the Geysers, confirms 

 this account, and also has told me that in no case did he see 

 anything in the form of a soft or gelatinous deposit of silex in 

 the neighbourhood of the springs, although he saw the Great 

 Geyser more than once in full action. Certainly if there be any 

 place in the world where we should expect to find this gelatinous 

 form of silex deposited in a natural condition, it is there, where 

 the waters are so high in temperature and so abundantly charged 

 with the earth in solution, and yet nothing approaching to it has 

 ever been observed by the most enlightened and observant visitors 

 of the spot. From our o^vn knowledge of nature, therefore, we 

 may reasonably arrive at the conclusion that such a natural con- 

 dition of silex as the gelatinous one is no more to be expected 

 than that we should find pure potassium or sodium occurring in 

 the bowels of the earth, or any other such substance which is the 



