348 
THE GEOLOGIST. 
■which one month 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 Chab^site 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 Ifature 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 tlie following lines, 
to what an extent water seems to have been active in the metumorphic 
transformations so perseveringly studied by this geologist. We have 
already mentioned the latter author's observations on the metamorphism 
of carboniferous rocks of every description, and also the results of his 
researches on the transformations of limestone rochs and strata, under the 
influence of eruptive or plutonic rocks.* In the work of which we 
speak here, argillaceous and sandstone rochs are studied from the same 
point of view. The latter, under the modifying influence of eruptive 
trap-basalt, dolerite, &c., present many phenomena well worthj^ 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 different sandstones. At other times they are seen as microscopic 
nodules, and often in perfect crystals, lining the cavities of the siliceous 
rocks. 
° The Geologist for February and June, 1858. 
t Flint is imdoubtedly of aqueous origin. — T. L. P. 
