166 Miscellaneous. 



In chert from the greensand of Fovant, Wilts, and from Lyme 

 Regis, Mr. Bowerbank found a similar but coarser texture ; and also 

 in chert casts of Spatangi from the greensand near Shaftesbury, 

 In chert from Portland and Tisbury he found similar cellular tissue, 

 but larger, and in texture more like the modern freshwater sponge. 



Mr. Bowerbank supposes the organic matter of the sponges and 

 zoophytes to have afforded to the silex stronger centres of attrac- 

 tion than were offered by the siliceous spicula of the sponges ; and 

 there is a geological consideration which seems to favour the hy- 

 pothesis, of the siliceous matter of chalk flints whilst in a semifluid 

 state having been segregated from the compound mass of lime and 

 silex of the nascent chalk beds, by the attraction of some organic 

 body, in the facts that the upper region of the English soft chalk, 

 which most abounds in flints, is nearly pure carbonate of lime ; whilst 

 the lower region of the hard chalk is usually destitute of flints, and 

 has silex diffused throughout its entire substance*. I cannot, how- 

 ever, but think there is something too exclusive in Mr. Bowerbank's 

 theory as to the universal presence of parasitic sponges in the ex- 

 ternal crust of every chalk-flint, and which admits of no case in 

 which an Alcyonium or any kind of extraneous body in chalk may, 

 without the co-operation of a sponge, have become externally in- 

 vested with a crust of silex of the same kind with that which he 

 allows to have been attracted to corallines and alcyonic bodies by 

 the animal matter they contained. 



MICROSCOPIC SHELLS. 



Mr. Tennant has informed me that a microscopic examination of 

 the Stonesfield slate by Mr. Darker, and of other oolites, has re- 

 cently shown them to be crowded with remains of organized bodies, 

 invisible to the naked eye. I learn also from Mr. Tennant that 

 abundant microscopic organic remains have recently been discovered 

 in thin slices of certain beds of carboniferous limestone from Derby- 

 shire ; similar results may shortly be expected from a microscopic 

 examination of the chert of the same formation. We must not 

 however be tempted by these discoveries to rush suddenly to the 

 rasli and unwarranted conclusion, that all limestone and all silex is 

 of organic origin. 



It has not yet been shown that the granules resembling the roe of 

 fishes, which give character to the oolite formation, and abound oc- 

 casionally in limestones of the triassic, carboniferous, and silurian 

 series, have any necessary connexion with organic bodies. We may 

 with Ehrenberg admit and admire the extent of microscopic cham- 

 bered shells and Infusoria, which he has shown so largely to pervade 

 the chalk and other calcareous and siliceous formations, without 

 claiming an exclusively animal origin for the entire substance of all 

 rocks in which lime or silex are the principal ingredients. 



[* " We observed no vestige of flints in the limestone at Seedrapett, and 

 all the fossils there consist of carbonate of lime, and eflfervesce freely with 

 acid ; but the vast quantity of silicified wood in the neighbouring formation 

 of red sand, seems to point to some phsenomenon similar to what must have 

 existed during the deposition of the cretaceous beds of Europe." — Mr. Kaye 

 on the Fossiliferous Beds of Pondicherry, Calcutta Journ. Nat. Hist., No. 6.] 



