Structure, and Formation of Beekite 97 



by what agency was this change effected ? Mr. Kesteven extends 

 the suggestion made in the Report of the Commission of the 

 French Academy of Sciences on Water-glass, concerning the origin 

 of flints, agates, petrified woods, &c, and applies it in the case 

 of Beekites. In these instances a slow decomposition of an 

 alkaline silicate by means of carbonic acid is supposed. Mr. 

 Kesteven thus describes his theory : — " Fragments of coral, 

 broken by the waves, and deposited with the beach now consti- 

 tuting rocks of red conglomerate, would retain a certain portion 

 of chlorides, while their decomposition would liberate the carbonic 

 acid which would separate the alkaline constituent of siliceous 

 springs, and cause the deposition of silica upon the nucleus of 

 coral. That a similar siliceous deposition is not found upon the 

 surrounding deposits is satisfactorily explained by the non-libe- 

 ration of carbonic acid from the pebbles, into the composition of 

 which its elements did not enter. This view is strengthened by 

 the fact of the non-silicification of the nucleus itself, the silicate 

 being arrested on its surface by the escape of carbonic acid. 

 Furthermore, where chalcedony presenting the Beekite characters 

 has been found upon stone, it has been limestone, from which it 

 is possible carbonic acid may have been disengaged at the time 

 of deposition. The characters of chalcedony, as presented in 

 Beekites, moreover, approach very closely to those of the siliceous 

 incrustations of the Geyser springs in Iceland." 



Mr. Pengelly's view is as follows. He says, " It seems pro- 

 bable that after the formation of the triassic conglomerate, some 

 of the calcareous pebbles in it underwent decomposition, that 

 water holding chalcedony in solution, and passing through the 

 rock, deposited the chalcedony on the nucleus : the nucleus in 

 some cases continued to decompose, by which it was wholly or 

 partially detached from its envelope, and not unfrequently re- 

 duced to dust. Suppose the decomposition to have commenced 

 at various points or centres on the surface of the pebble, the 

 chalcedony deposited at these points would form central tuber- 

 cles; let the decaying process extend from and around these 

 centres, the chalcedony deposited around these centres would 

 form a ring," — and so on. 



Mr. Pengelly states in the paper just referred to, that " the 

 interior of the Beekite is calcareous," and that " the nucleus 

 appears to be always a fossil, and is either a sponge, a coral, a 

 shell, or a group of shells The organic structure is fre- 

 quently preserved on the inner or concave surface of the enve- 

 loping crust, even when the nucleus is reduced to powder. Oc- 

 casionally organic traces are discernible on the exterior surface 

 of the chalcedony; but such cases are not frequent. Some of 



Phil. Mag, S. 4. Vol. 23. No. 152. Feb. 1862. II 



