538 Dr. T. Sterry Sunt — On Italian Geology. 



farther, " I will not assert that when specimens of this newer gneiss 

 are confusedly mixed with those of the more ancient, it would always 

 be practicable to distinguish them petrographically ; but I do not 

 hesitate to affirm that their distinction in the held is not difficult ; on 

 account of the frequent alternation of the younger gneiss with the 

 other characteristic rocks of the upper series [micaceous and horn- 

 blendic schists, etc.], while the older gneiss, however wide its 

 extent, is generally unmixed with other rocks." 



Above this recent gneissic and mica-schist division, but below the 

 anthracitic group, and included in the "newer crystalline series" of 

 Gastaldi, there is a considerable thickness of crystalline schists, often 

 soft and iinctuous, and variously described as argillaceous, talcose, 

 and micaceous, or as grey lustrous schists, which are sometimes 

 sericitic. These, moreover, include quartzite, karstenite, dolomite, 

 and banded and statuary marbles, with occasional serpentines and 

 amphibolic rocks. Serpentines are also met with in intimate asso- 

 ciation with the younger gneisses, and hence Gastaldi often spoke of 

 the whole triple group of the newer crystalline series above the 

 ancient gneiss as the " pietre verdi zone." To each of these three 

 divisions he, in common with other Alpine geologists, assigns a 

 thickness of several thousand metres. 



While these great divisions of the crystalline' rocks were thus 

 being defined in the Western Alps, Von Hauer had already, in 

 1868, shown the same succession further to the eastward, in the 

 Lombardo- Venetian Alps, where he distinguished, first, the ancient 

 gneissic and granitic rocks, called by him the central gneiss ; 

 second, a great thickness of green rocks or pietre verdi, including 

 serpentine, euphotide, and diorite, with various amphibolic and 

 chloritic rocks, together with saccharoidal limestones ; and, third, 

 a recent gneiss and mica-schist series. Gastaldi, at an early 

 date in his studies, recognized in the older or central gneiss the 

 Laurentian series of North America, and in the succeeding green 

 rocks, or pietre verdi proper, the group which I had in 1855 called 

 Huronian. It was not until 1870 that I attempted to define as a 

 distinct and newer series the group of younger gneisses and mica- 

 schists in North America, called by me subsequently, in 1871, the 

 White Mountain or Montalban series, and corresponding both 

 lithologically and stratigraphically to the recent gneiss and mica- 

 schist series already recognized in 1868 by Von Hauer in the Eastern 

 Alps, indicated by Gerlach in the Western Alps in 1869, and 

 described more at length by Gastaldi in 1871. The work of none of 

 these was known to me when, in 1870, 1 first set forth the distinctness 

 of this great group of younger gneisses and mica-schists in North 

 America, and also indicated their existence in the Scottish Highlands. 



I had, in 1881, an opportunity of examining this upper gneissic 

 series in the Western Alps, near Biella in the province of Novara, 

 and in company with Quintino Sella (who with Berutti had carefully 

 mapped the region), of going over a section which had been studied 

 and described alike by Gerlach and by Gastaldi. Here, besides the 

 ancient gneiss, with included graphitic and pyroxenic limestone, the 



