250 Mr. J. S. Bowerbank on the Siliceous Bodies of the Chalk, 



I have observed f^ and granting this^ I have really very little more 

 to desire, as the whole of the views exhibited in my paper are 

 attempts to elucidate obscure natural phsenomena and not mat- 

 ters of theory ; but as in the course of his reasoning upon the evi- 

 dence which I have produced of the organic origin of the siliceous 

 bodies in dispute, he has referred to natural historical facts in 

 support of his views, and ventured upon assertions based upon 

 these facts which are unfortunately not correct, I should not 

 be doing justice either to the subject or myself if I were not to 

 endeavour to correct these misapprehensions. 



The author, after noticing the difference in the views of the 

 formation of chalk flints entertained by Prof. Ehrenberg and 

 myself, proceeds thus* : " It may be allowed to us, in all humility, 

 to call in the aid of other classes of facts to clear up the mystery, 

 and this I now proceed to do. I fully admit that spiculse are not 

 uncommonly found in some flints, but they are most assuredly 

 not always found ; in some flints they are very numerous, while in 

 others from the same spot they are exceedingly rare, and in very 

 many wholly wanting. Now these sponge spiculse are indestruc- 

 tible. The destruction of the structure of the sponge, which this 

 theory requires as a necessary postulate, would not destroy them. 

 How then is it that they are thus variably present ? And it is 

 important to remember that similar spiculse are found in the 

 chalk itself.^' In the first place, I deny totally that the destruc- 

 tion of the structure of the sponge is a necessary postulate of 

 what the author designates as my theory. I have never under 

 any circumstances made such an assertion, and if I had, it would 

 have been a most egregious blunder ; for the remainder of the 

 passage I may simply say, that the conditions of the structure of 

 the skeleton and the spicula are precisely those which every natu- 

 ralist acquainted with the Spongiadse would expect ; for although 

 the horny skeletons of the Spongiadse are very enduring, the 

 gelatinous interstitial substance of the sponge, which in life 

 abounds with spicula, is exceedingly destructible, and is dis- 

 solved away from the skeleton almost immediately after the death 

 of the animal; and in many species of Halichondria this is so ra- 

 pidly effected, that a specimen taken fresh from the sea and placed 

 in the hand can scarcely be retained there many minutes without 

 its being flooded with the gelatinous matter shed by the animal, 

 and this equally takes place if the sponge be placed in a small 

 basin of salt water ; in a few hours it will have shed the whole of 

 its interstitial gelatinous matter, the dead skeleton only remaining. 

 What is more natural then, than that in the silicified remains of 

 sponges, in which the skeleton has always to a great extent been 



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