15 



HiSTORT OF THK INQUIRY. 



These flinty concretionsliaving.as I have said, aroused so much 

 interest in minds curious about such things, let me glance for a 

 few minutes at the history of the inquiry itself, as given by 

 Sollas in his paper on " Affinities of the Genus Siphonia/ 

 1665. The first notice of them that is to be found is in Aubrey's 

 "Natural History of Wiltshire," under the date 1665 : " I 

 desired Dr. William Harvey (the discoverer of the circula- 

 tion of the blood) to tell me how flints were generated, he 

 sayd to me, ' That the black of the flint is but a natural 

 vitrification of the chalk.' " An answer of the great doctor 

 which betrayed considerable ignorance both of the nature of 

 chalk and of the nature of flint, glass, and of a great deal 



1751. Guettard declares them to be sponges and corals— he 

 evidently mistook a branching sponge for a coral. 



1758 In 1758 Baier talks of fossil figs as " lusus naturae, but 

 in another part of his work refers them to marine vegetables. 



1 769. In 1 769 Walch speaks of these " corjelline figs " as manne 

 mushrooms. . 



1770. In 1770 Guettard comes to the conclusion that they were 

 formed by polyps. , , -^ tt 



1822. In 1822 Mantell referred them to the alcyonites. Me 

 gave the name choanites to a genus, a name long retained, 

 and figured to himself a curious creature swimming about 

 by the aid of many tentacles and rushing away from the 

 petrifying fluid which suddenly entered his home, and by 

 which it eventually became changed into flint. 



1833. It was Bowerbank, however, who finally placed the 

 sponge theory on a firm basis and showed how the forms 

 of the spicules were determinative of the species and genera 



of sponges. i- •/. j 



He, however, attempted to show that flints were sihcified 



HORNY sponges— the horny sponge being of the kind we associate 



with the bath. 



Sponges, therefore, having by the concurrent testimony ot 

 all later observers played a prominent part in the formation of 

 flints, it behoves us to devote a little time to the consideration ot 

 their structure and physiology. 



What is a Sponge? 



A sponge, according to Dr. G. J. Hinde, in the ordinarv 

 acceptation of the word, is the internal framework or skeleton of 

 an animal whose soft vital parts are composed of cellular proto- 



