THE GEOLOGIST. 



M hich one mojith was not deemed too long a period for one experiment 

 The mineral water of Plombieres acts upon the masonry by the alkaline 

 silicates it contains, and forms Zeolites in abundance. These crystallize 

 at a temperature which is inferior to 60 degs. (centigrade), consequently 

 under the simple pressure of the atmosphere, and almost at the surface 

 of the soil. The crystals of Chabasite are always found in the bricks, 

 the Apophyllite exclusively in the lime, which circumstance is in perfect 

 accordance with the natural composition of each, and shows that their 

 elements have not been totally brought by the water, but partly 

 furnished by the cement. Hence the conclusion, that the same 

 dissolution, acting upon masses of different nature, developes in each 

 distinct combinations," arrived at by M. Daubree. This geological 

 formation, which at Plombieres is taking place under our eyes to a 

 certain limited extent, has doubtless been accomplished in bygone ages 

 to an immense extent. It is evident that many eruptive rocks must 

 have been penetrated by water during the period of their cooling, and 

 on a far larger scale, at a higher temperature, and under a much greater 

 pressure than at the miniature laboratory, which I^ature seems to have 

 opened for the benefit of her pupils, at Plombieres. 



We have collected together the most important facts contained in M. 

 Delesse's new Memoir on Metamorphism, for the purpose of relating 

 them here, as it will be seen, if we mistake not, in the following lines, 

 to what an extent water seems to have been active in the metamorphic 

 transformations so perseveringly studied by this geologist. We have 

 already mentioned the latter author's observations on the metamorphism 

 of carboniferous rocJcs of every description, and also the results of his 

 researches on the transformations of limestone rocks and strata, under the 

 influence of eruptive or plutonic rocks.'^* In the work of which we 

 speak here, argillaceous and sandstone rocks are studied from the same 

 point of view. The latter, under the modifying influence of eruptive 

 trap-basalt, dolerite, &c., present many phenomena well worthy of 

 being recorded. Let us consider, first, the siliceous rocks : — 



We find that their metamorphism, like that of limestone, is 

 characterised either by the formation of certain minerals, or by peculiar 

 modifications in their structure. Amongst the minerals thus formed are 

 hydrated oxides of iron and of manganese, and certain carbonates, 

 principally carbonate of lime, dolomite, also carbonates of magnesia and 

 iron, sometimes silica. Among hydrosilicates ferruginous clay, and 

 especially Zeolites, are formed. Green-earth is seen penetrating sand- 

 stones, to which it gives its colour, but their quartz remains as transparent 

 as before, and comparatively unchanged. This metamorphism has been 

 particularly favourable to the formation of Zeolites, which are seen to 

 have been thus formed in the most compact of sandstones, and are even 

 met with in common flint. f In most cases the Zeolites form a sort of 

 white cement, tilling up the small cavities between the grains of quartz 

 in diff'erent sandstones. At other times they are seen as microscopic 

 nodules, and often in perfect crystals, lining the cavities of the siliceous 

 rocks. 



o The Geologist for February and June, 1858. 



t Flint is undoubtedly of aqueous origin. — T. L. P. 



