46 DR- THOMAS STERRY HUNT ON THE 



itself was made of fragments of burnt red brick, with others of sandstone and of a friable 

 granite, the whole in a calcareous cement. Eepairs having required cuttings to be made 

 in this mass, it was fovind to contain numerous crystallized mineral species, formed through 

 the action of the water, which were examined by Daubrée, with the aid of de Senarmont 

 for the crystallographic determinations, and first described in 1858. 



§ 91. The substance of the fragments of brick was found to be altered to some depth, 

 while the numerous cavities therein were lined or filled with various matters, often dis- 

 tinctly crystallized. Among these were identified chabazite and i:)hillip8ite (christianite), 

 gismondite, implanted on the chabazite, scolecite, and what is designated by Daubrée as 

 mesotype (thomsonite or natrolite). In the calcareous cement were well-defined crystals of 

 apophyllite containing, as usual, a little fluorine ; while in cavities in the lower jîart of the 

 concrete, near the gravel, was found an abundant gelatinous matter, which was detected in 

 the act of deposition, in recent cuttings in the mass through which the water was still 

 oozing. This matter elsewhere had consolidated into a white mammillary concretionary 

 fibrous substance, which was found to be a hydrous silicate of lime, with but 1.3 hundredths 

 of alumina, and constitutes the pectolitic species, plombierite, already noticed (§ 84). 

 With the various minerals in the concrete was also found an abundant deposit of silica in 

 the form of hyalite, and more rarely crystals of tridymite, and globules of chalcedony, 

 together with calcite in well defined crystals, arragonite, and fluorite. The chabazite was 

 'often found adherent to fragments of wood enclosed in the concrete, recalling, as observed 

 by Daubrée, the similar occurrence of zeolites with fossil wood in lacustrine limestone in 

 Auvergne. The various minerals named were absent from the fragments of friable granitei 

 while in the underlying gravels the only matter deposited was an amorphous aluminous 

 silicate, compared to halloysite, and found also in the concrete. 



§ 92. The fragments of red burnt brick in the cement had undergone an alteration from 

 their surface, marked by concentric lines of changed color, as well as by the development 

 of zeolites, and also of an amorphous matter compared by Daubrée to palagonite. In 

 these fragments, the amount of combined water had increased from two or three hun- 

 dredths in the centre, to eight hundredths in the outer infiltrated portion, in which 

 the amount of matter soluble in nitric acid was equal to fourteen or fifteen hun- 

 dredths, including a notable proportion of potash, supposed by Daubrée to have been fixed 

 from the waters. The silica, alumina and lime of the new mineral species were 

 derived from the cement and the bricks, the calcination of which had probably rendered 

 them more susceptible to chemical change. As has been pointed out by Daubrée, the resem- 

 blance between these species and the similar ones found in many rocks, extend even to 

 minor details of crystalline form and association. The small géodes lined with crystals, in 

 the bricks, as the writer can testify, cannot be distinguished by inspection from many 

 similar cavities in certain amygdaloids. 



§ 93. Similar phenomena have since been noticed in the ancient constructions around 

 the thermal waters of Luxeil, Bourbonne, and others in France, and at Oran in Algeria, 

 These localities have added little more to our knowledge of the production of silicates, 

 though at some of them, and notably at Bourbonne, besides zeolites, have been found 

 various crystalline metallic sulphides derived from the transformation of metallic objects 

 enclosed in the concrete. The water of the last named locality, which unlike that of 

 Plombières, rises from the muschelkalk, has a temperature of about 60' C, and is 



