Sollas — A Contribution to the History of Flints. 



3-96838 grammes, the weight of a volume of flint equal to that of 

 the sponge. Weight of the ignited spicules, 0*6658 grammes : 



0-6658 v 3-96838 = 16-77 per cent. 



Anthastra pyriformis thus contains 16*77 per cent, of the 

 quantity of silica required to convert it into solid flint. Ex- 

 pressed as a common fraction, this is the -§-, so that it would require 

 six equal and similar sponges to furnish sufficient silica for the 

 conversion of one of them into flint. 



The percentages in the following Table have been obtained by 

 the method just described, from such sponges as resemble those of 

 which skeletal remains are actually found associated with flint. 



Table sJwicing the percentage of Silica present in various species of 

 Sponges, the weight of a volume of Flint equal to that of the 

 Sponge being taken as 100 : — 



Anthastra communis, Sollas, . . 5-05 



Anthastra pyriformis, Sollas, . . 16*77 

 Pachastrella abyssi, O. Schmidt, . 3*9 



Cydonium hirsutus, Sollas, . . . 17*5 

 Cydonium pachydermata, Sollas, . 9*9 

 Tethya maza, Selenka, .... 7*4 

 Cinachyra barbata, Sollas, . . . 5*5 

 Azorica pfeifferae, Carter, . . . 6*44 



Corallistes masoni, Bowerbank, . 14*6 



Vetulina stalactites, O. Schmidt, . 25*0 



Theonella swinhoei, Gray, . . . 12*4 



(mean of 3 determinations). 



(mean of 3 determinations). 



(taken from a skeleton), 

 (from a skeleton). 



The mean of these results is 12*22 per cent. 



And since 100 4- 12-22 = 8*18, we may say that it would on an 

 average require 8*18 sponges to produce sufficient silica to make a 

 flint of the size of one of them. 



We may now attempt to form a rough estimate of the period 

 of time required to produce the material of a bed of flints. The 

 experiments made on sponge culture in the Adriatic and the Florida 

 Gulf showed that it takes from five to seven years for a bath sponge 

 to grow from about one cubic inch to a saleable size. Now the size 

 of a saleable sponge is not very different to that of an average-sized 

 flint nodule; and assuming that the rate of growth of siliceous 

 sponges is not very different to that of bath sponges, we may make the 



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