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



in opposition to the figured side also to be explained, and more- 

 over the author does not give us any principle upon which these 

 minute currents can be accounted for. 



In treating of the probable origin of these figured specimens 

 the author says * : " The movement which caused this fracture 

 and impelled the pieces on to the yet fluid mass was probably the 

 same which caused the whole surface on which the fractured 

 pieces alighted to slip forwards, and which surface and the mass 

 beneath it, probably by the very agitation thus caused, instantly 

 solidified, leaving the ridge a b, and fixing the fractured pieces 

 firm. 



'^ This case illustrates and demonstrates all the conditions al- 

 ready noticed ; extreme liquidity and rapid solidification of the 

 flint, together with the soft state of the surrounding chalk. ^' 



Here the author distinctly recognises the theory of the gelati- 

 nous condition of flint, although he appears in the commence- 

 ment of the paper to have repudiated it, and in the following 

 page he says f '- " Where organic remains of any considerable 

 size, or grouped in particular masses, happened to be abundant 

 and lie near one another, they acted as separate centres, while 

 the solution was attracted to them in a mass.^' I must confess 

 that this mode of accounting for the fantastically-formed nodules 

 of flint is perfectly incomprehensible to me. I cannot by any 

 stretch of the imagination conceive a mass of saturated solution 

 of " extreme liquidity '' preserving its integrity for a moment at 

 the bottom of the ocean, and especially amidst so many minute 

 currents as the author supposes to exist. But let ns see what 

 foundation we have for the supposed " masses ^^ of solution of 

 silex. 



Throughout the whole of the report of Dr. Turner^ s lecture, 

 there is nothing touching the existence in nature of a gelatinous 

 condition of silex beyond the supposition of Brongniart that such 

 might be the case, and which is expressed thus J ; "In the forma- 

 tion of chalcedony and flint, it was most likely, as Brongniart sup- 

 posed, that the silica, as in operations in the laboratory, was depo- 

 sited in a gelatinous form, hardening gradually by evaporation 

 and the cohesive attraction of its particles.^^ By the use of the 

 word evaporation it is evident that the passage is not applicable 

 to the conditions of silex in solution in the depths of the ocean. 

 The author then proceeds thus : " The regularly disposed lines 

 which were so beautifully displayed in some varieties of chalcedony, 

 seemed owing to successive deposition — one layer succeeding an- 

 other, each assuming the form and irregularities of the preceding, 



* Page 15. t Page 16. 



X Loudon and Edinb. Phil. Mag. vol. iii. p. 27. 



