Structure, and Formation ofBeekite. 101 



of several Beekites in which no lime whatever was found. Their 

 composition scarcely differed from that of flint, except in the 

 larger per-centage of iron which they contained. 



The chemical causes concerned in the formation of Beekite 

 appear to me of peculiar interest. It is reasonable to believe 

 that the removal of carbonate of lime from a shell or a coral, and 

 its replacement by silica, has been effected by the agency of 

 water holding carbonic acid and silica in solution together. Such 

 solutions occur frequently in nature, not only in springs like 

 those in the neighbourhood of the Iceland Geysers, but in several 

 places in Great Britain, — silica being, indeed, an almost invariable 

 constituent of common waters. We may argue, then, that such 

 a solution filtering through the debris of organic forms, not only 

 removes their carbonate of lime by virtue of the solvent power 

 of its carbonic acid, but deposits some silica instead. This sup- 

 position has been tested and confirmed by experiment. A frag- 

 ment of a recent coral was fitted into the neck of a funnel, and 

 a 1 per cent, solution of silica (prepared from silicate of potash 

 by Graham's dialytic method), containing a little carbonic acid 

 gas, was allowed to drop slowly on the coral and filter through : 

 after a time the liquid ceased to pass. The filtrate contained no 

 silica, but much carbonate of lime. The fragment of coral had 

 lost nearly all its lime, but had retained its structure in great 

 measure ; it was, however, covered with a thick film of gelatinous 

 silica, and was very soft. In such a reaction as this, it is not 

 unlikely that a small portion of lime would be retained as sili- 

 cate. Where the process of silicification has gone on to its com- 

 pletion, we have a tolerably exact reproduction in silica of the 

 original organism, the result beiug, in the case of corals, 

 sponges, &c, a light hard porous mass, occasionally hollow, of 

 chalcedony. But where the process has been arrested by the 

 stoppage of the flow of the siliceous solution, the central portions 

 of the Beekite have retained nearly their original composition as 

 well as structure ; and in some rare instances it would seem that 

 a subsequent deposition of carbonate of lime, in the spaces not 

 occupied by silica, had taken place. 



II. Of the physical aspect of Beekite, the quotations made in 

 the earlier part of this paper, taken in connexion with the 

 illustrations in Plate III., will give some idea. The mammilla- 

 tions and concentric ridges (figs. 1-4,9 & 13), though frequent, 

 are not invariably present. Besides the organic structure (shown 

 more or less distinctly in figs. 2, 9, & 10-12), Beekites often 

 display one or more lines and furrows on their surface, quite 

 independent of the mammillations. These lines indicate for the 

 most part certain planes of cleavage or fracture, as shown in the 

 upper and lower sides of fig. 2 and the light side of fig. 3. 



