192 Proceedings of the Royal Physical Society. 



A little later than the time when Celadonite has begun to 

 coat the interior of the cavity, weak solutions of silica-jelly, 

 in a form which is destined to become Chalcedony, begin to 

 be carried in by osmosis in the same way as the Celadonite 

 was before. There is abundant evidence to show that this 

 stage of agate-formation was often accompanied by a rupture 

 of the previously formed layers of Celadonite, by the ingress 

 of the solutions containing the Chalcedony. The saponaceous 

 nature of the Celadonite seems to have been very favourable 

 to its easy removal. As a consequence, shreds and ragged 

 filaments of the ivy-green mineral were gradually torn from 

 the walls of the cavity, and eventually became coated with film 

 after film of the silica-jelly, until, in the end, the filaments of 

 Celadonite became completely enveloped within the chalcedo- 

 nic material. Eventually the solvent of the Chalcedony began 

 to escape, the material coagulated, and finally hardened, and 

 then the filaments of the ivy- or moss-green Celadonite became 

 enveloped in the Clear Chalcedony and thus simulated moss. 



All true Moss Agates were thus formed. Mochas are 

 different in origin, and will be described further on, in their 

 proper place. 



More usually the " priming " of Celadonite is not coated 

 directly by the Clear Chalcedony Layer just mentioned, for the 

 felspars present in the rock have usually begun to give way at 

 a stage closely following that of the initial stages of destruction 

 of the ferromagnesian silicates. These products of decom- 

 position of the felspars were carried in through the rock, 

 through the walls of the cavity, and thence through the 

 layer of Celadonite, by osmosis, which carried in the solutions, 

 and deposited them, and which, in turn, also favoured the ex- 

 pulsion of the aqueous solvent after it had deposited its load. 

 By this partial destruction of the felspars, and the redeposi- 

 tion of the dissolved material in a solid form, a layer of Zeo- 

 lites was deposited. The precise nature of the Zeolite must, 

 of course, have varied with the nature of both the solvent 

 and the material acted upon. In Scottish Agates, Natrolite 

 and Heulandite seem to be the commonest of these ; though 

 there can be no doubt that other species were formed in 

 exactly the same manner. 



