1856.] MORRIS — ALLOPHANE. 13 



within, or moulds outside of these. In this way we have often 

 dehcate casts of crabs, lobsters, and molluscs, in which every atom 

 of the original material has disappeared, — the internal structure has 

 vanished, and a very perfect cast of the exterior remains. 



The mangrove-roots prevailing in the blue clay are everywhere 

 perforated by the holes of the Pholas, or some other horer. The per- 

 forations seem all at first to have been lined with a beautiful crust of 

 calcareous sinter, varying from a few lines to a tenth of an inch in 

 thickness. The structure of the whole, when broken across, is cry- 

 stalline, arranged in ten, twenty, or thirty fine layers, slightly pinkish, 

 and somewhat differing from each other in tint, and arranged like 

 the striae of satin-spar. This crust appears to have been produced by 

 the percolation of water charged with lime. 



Here once more a similar transformation to that previously de- 

 scribed appears. A little of the surrounding clay seems at first to 

 intrude itself, and, gaining volume and consistency, first fills up the 

 crystallized tubes in front, and, the limestone gradually disappearing, 

 finally remains in its place as a perfect cast of the original boring. 

 All degrees of the transformation are found in abundance. 



2. On the Occurrence o/Allophane at Charlton, Kent. 

 By J. Morris, F.G.S. 



For some time past a substance, having at first sight the appearance 

 of amorphous carbonate of lime, has been noticed as occurring at the 

 chalk-pit near Charlton, and to which the workmen applied the term 

 "petrified water." It was found in more abundance than at present 

 during the progress of the old workings through some parts of the 

 pit, although it is still to be obtained. 



This substance, which has been carefully analysed by Mr. Dick, of 

 the Metallurgical Laboratory of the School of ]\Iines, Jermyn Street, 

 proves to be allophane, which has not, I believe, hitherto been re- 

 corded as a British mineral. A brief notice of its mode of occurrence 

 may therefore be useful to those who are interested in the formation 

 of minerals, and may possibly stimulate some farther inquiry as to its 

 origin. 



Allophane and the alHed species are hydrous silicates of alumina, 

 which diifer in the relative quantities of silica, alumina, and water 

 they contain, the latter ranging above 40 per cent, in scarbroite and 

 allophane. 



The nature and position of these minerals would seem to indicate 

 that their origin is due to the slow action of chemical and other 

 agencies upon the rocks with which they are associated, or more 

 generally, as in the present case at Charlton, on the strata superposed 

 to the rock in the fissures of which latter the mineral is deposited. 



The Charlton pit exposes from 15 to 20 feet of chalk-with-flints, 

 which is traversed, independently of joints, by numerous fissures, 

 ranging nearly in a north and south direction (N.N.E. by S.S.W.) ; 



