DELESSE ON CRYSTALLINE LIMESTONES. 29 



beds (argilolites), which certainly have not been melted, and the 

 stratification of which is quite recognizable. At Morel, in the Com- 

 mune of St. Laurent (Saone-et-Loire), crystals of pink orthose, of an 

 after-development, exist in a limestone with Gryphcea arcuata, which 

 has a crystalline structure, but characterized by a greyish yellow tint 

 somewhat diiferent from its usual colour. Lastly, at Steiumal, fel- 

 spar-crystals have been observed by M. von Dechen in the inside of 

 the abdominal buckler of a Homalonotiis. In the same manner, the 

 Transition greywackes in the neighbourhood of Thann and to the 

 south of the Vosges are very often completely impregnated with fel- 

 spar, and still we find in them numerous remains of plants which 

 have been well preserved in spite of the later development of crystals 

 of felspar of the sixth system. 



The intimate and mutual penetration of the limestone and gneiss 

 shows that both have been reduced to a plastic state, if not to actual 

 fluidity ; and the dissemination of the felspar in the limestone mass 

 shows also that the gneiss must have been suflSiciently pasty for the 

 felspar to have been secreted. 



The penetration of the limestone by the gneiss, as also the undu- 

 lations sometimes presented by both rocks at the line of junction, 

 make it evident that pressure was brought into play to a great extent 

 during the crystallization of the gneiss ; this has produced in the 

 limestone fissures generally parallel to its line of contact with the 

 gneiss, and comparable to those formed in a book, the leaves of which 

 are squeezed or pressed back laterally. These fissures have been im- 

 mediately filled by the secretions of matter diffused in the limestone, 

 and they have given place to the parallel zones of nodular concre- 

 tions*, whilst the same matter formed the veins or the lining in fis- 

 sures of the gneiss. Although in most of the metamorphic limestones 

 the minerals are especially developed in the natural joints originating 

 in stratification, these nodules, on the contrary, in the limestone of 

 the gneiss of the Vosges, apparently owe their parallelism to pressure. 



Pressure, like heat, has been also effective in actuating molecular 

 attraction and in developing the different minerals disseminated in 

 the limestone. 



Subsequently to the crystallization of the limestone and of the 

 gneiss certain minerals have been, and probably are still being modi- 

 fied by chemical action arising from infilti'ation, so that new minerals 

 are formed by pseudomorphosis ; as for example, the pyrosklerite. 



[T. R. J.] 



On the Formation o/" Crystallized Minerals. 

 By Aug. Drevermann. 



[Annalen der Chemie, 1853, vol. Ixxxvii. p. 120.] 



A series of experiments vnth which I have been lately engaged 

 seem to throw some light on the formation of crystallized minerals 



[* Vide supra, p. 21.] 



F 2 



