290 EXPERIMENTS ON METAMORPEISM AND 



temperature at which they are reputed to be insoluble in it. At 

 points as near each other as a few sixteenths of an inch we see dif- 

 ferent products forming, according to the nature of the substance on 

 which the water acts. Thus it is that apophyllite, a silicate contain- 

 ing lime as well as potash, crystallizes in the cavities of the lime. I 

 have never met with it in the brick. It is, on the contrary, almost 

 exclusively in the cavities of this last that we find chabasite, a double 

 silicate of alumina and pctash. The same solution, therefore, attack- 

 ing rocks of different natures, develops combinations special to each 

 of them. Such a marked localization of certain zeolites appears to 

 show that their elements were not entirely contained in the water 

 imbibed by the masonry; it only contributed a part. The comple- 

 mentary elements necessary to the composition of the new minerals, 

 lime, alumina, and others, were contained either in the mortar or in 

 the bricks which gave them up to the water. 



While the bed of concrete abounds in zeolites, the alluvial sand 

 over which the masonry was built presents no indication of the for- 

 mation of these silicates, although the thermal water traverses it be- 

 fore reaching the concrete. It confines itself to depositing between 

 the interstices of the pebbles a yellowish argillacious mass, which is 

 one of those imperfectly defined substances known under the name 

 of chemical clays or halloysites. This contrast shows further that 

 the zeolites are not the first deposit of the thermal water, but that it 

 is produced only by the reaction of this mineralized water on other 

 silicates. 



"What is going on at Plombieres has been evidently accomplished 

 on a wide scale in certain geological formations. The collection of 

 minerals disseminated in the innumerable cellules of the masonry,' 

 the zeolites, opal, and arragonite, constitutes an association which is 

 frequently the appendage of certain eruptive rocks. Furthermore, 

 the whole of the conditions under which these contemporaneous min- 

 erals exist recall, in the most minute particulars, their disposition in 

 the layers of basalt and trap, which have an amygdaloidal structure. 

 If it were not for the difference of color it would be quite possible to 

 mistake the parts of this concrete which contain the zeolites for the 

 basaltic traps in which the same minerals have been formed. The 

 bricks, with their cavities and druses, surprisingly imitate amygda- 

 loidal rocks. Such an identity of results incontestibly indicates 

 striking analogies of origin. Near the volcanic rocks of Jiltna, of 

 Iceland, and other countries, we find a rock to which the name . 

 palagonite* has been given. This hydrous silicate is easily fusible, 

 gives a jelly with acids, has often a resinous aspect, presents the 

 strongest analogy with the silicates of Plombieres, and, according to 

 all probability, results from a transformation similar to that which gave 

 rise to these last. But it is especially with regard to metamorphism 

 that we should here state the results of the action of the springs at 

 Plombieres. 



* Kammelsberg;, Chemische Minerdlogit, 3d and 5th supplement, pp. 93 and 185 ; Annalet 

 des Mines, 6th series, vol. xii, p. 474. 



