22 GEOLOGICAL MEMOIRS. 



limestone is almost entirely composed of white Orthose-felspar, 

 brownish or blackish green Amphibole, Garnet, and Mica. In the 

 St. Philippe quarry the limestone with nodules is succeeded by a 

 micaceous limestone, which passes into a gneiss with Garnet, Horn- 

 blende, and Mica. This is succeeded by a gneiss traversed in every 

 direction by very irregular veins, often derived from the rock itself. 

 These veins consist of Orthose, Pyroxene, Oligoclase, Amphibole, and 

 Sphene. The first two are the most abundant (p. 175). 



Professor Hitchcock has described a gneiss occurring in Massa- 

 chusetts, which is accompanied by a great development of saccharoid 

 limestone. This gneiss, in which Pyroxene is occasionally associated 

 with Sphene, M. Delesse considers to be probably of the same age 

 as the gneiss of the Vosges. 



In the cavities of the St. Philippe gneiss, as well as in the druses 

 and in the veins of orthose, are found Albite, Actinote, Asbestus, 

 and Sphene ; and M. Delesse particularly refers to the great scarcity, 

 and even absence, of quartz in the veins and in the nodules, as wejl 

 as in the gneiss forming the roof of the limestone. 



Although the mineralogical composition of the vei7is in the gneiss 

 differs somewhat from that of the nodules, and although they further 

 diifer in the circumstance that the former are ramified and intimately 

 connected with the gneiss, and the latter are rounded and distinctly 

 separated from the limestone, yet, it must be noticed, the veins and the 

 nodules have the great proportion of their minerals in common, — 

 especially the Orthose, the Felspar with a greasy lustre, the Amphi- 

 bole, the Pyroxene, and the Sphene, Hence it is probable that they 

 were formed simultaneously and had the same origin ; and that the 

 differences they present in their position and constitution must be 

 attributed to the nature of their enclosing rocks respectively. Such 

 influence, moreover, was not exercised only at the moment of the 

 secretion and crystallization of the veins and nodules, but it has been 

 felt during the physical and chemical conditions to which the gneiss 

 and the limestone have been since submitted. The Pyrosklerite, for 

 instance, appears to owe its formation to pseudomorphic action de- 

 veloped by the intervention of the limestone. 



After some general notices of statuary marbles, and of the dolomite 

 in the gneiss of Maudray, M. Delesse proceeds to observe that he 

 considers the limestone and the enclosing gneiss as contemporaneous, 

 though it would be exceedingly difficult to determine the age of the 

 several rocks so situated with any exactitude. The saccharoid lime- 

 stones of the gneiss in the Vosges, United States, Scotland, and 

 Scandinavia are regarded by M. Delesse as being of the same age. 

 Lastly, he observes, that the minerals of the Vosges, many of which 

 have been formed simultaneously in the limestone and in the gneiss, 

 are unaccompanied by metallic minerals, and that consequently the 

 geological phsenomena by which they have been developed are inde- 

 pendent of those which in Scandinavia and elsewhere have produced 

 metalliferous ores in similar rocks. [T. R, J.] 



