Structure, and Formation of Beekite. 99 



diminished pebble, which in most cases continued to decompose." 

 Of what nature is the decomposition of limestone which is here 

 spoken of ? and how did it originate ? or did it occur at all? The 

 whole problem before us resolves itself into two parts, which it 

 will be better to examine separately. We have to account for — 



I. The chemical composition of Beekite; and 

 II. Its physical appearance. 



I. The chemical constituents of Beekite vary less both in 

 nature and proportion than the outward appearance of different 

 specimens would lead one to infer. I have been unable to find 

 more than one recorded analysis ; it is given by Mr. Kesteven in 

 the letter to which I have already referred, and is as follows. 

 A Beekite weighing 1040 grains contained, according to his 

 statement — 



grains. per cent. 



Carbonate of lime .... 470 . 45*20 



Chalcedony 540 . 51 '93 



Sesquioxide of iron and alumina 5 *46 



Carbonaceous matter, residue of 



animal matter of coral . . 25 2*41 



1040 100-00 



These results, which I presume are to be regarded as approxi- 

 mative only, must not be taken as indicative of the general 

 composition of Beekite ; for I have examined qualitatively or quan- 

 titatively nearly twenty specimens, and in only two cases have I 

 found more than 3 per cent, of carbonate of lime : even where 

 the appearance of the mass most forcibly recalled the original 

 coral, the proportion was no larger. In the two cases where 

 carbonate of lime occurred in considerable quantity, the Beekite 

 was singularly compact. Parts of one specimen did not show 

 the characteristic concentric ridges of chalcedony until the car- 

 bonate of lime in which they had been imbedded was dissolved 

 away by means of an acid ; while the other specimen, which is 

 given in PL III. figs. 10, 11, 12, although showing, when cut and 

 polished (fig. 10), or when in thin section (figs. 11, 12), a di- 

 stinct coral throughout, was enveloped in a siliceous coat, but 

 possessed a calcareous nucleus. In this case the portions of the 

 coral towards the exterior of the mass had been replaced by 

 silica, so far as the cell-walls of the polypidoms were concerned, 

 the cells being partly filled with carbonate of lime, the interior 

 portions remaining calcareous throughout. Occasionally a 

 Beekite is found containing a purely inorganic nucleus of lime- 

 stone, but in a large number of specimens there is actually no 

 carbonate of lime whatever, all the lime present being in the 

 form of silicate. 



H2 



