Dr. T. Sterry Hunt — On Italian Geology. 535 



divide the crystalline rocks into two great zones : the lowest con- 

 sisting of the oldest rocks of the Alps, and probably of the globe, is 

 that of the central, ancient, or primitive gneiss. It is emphatically 

 the zone of the orthoclase feldspar, and is very poor in minerals. 

 The other zone is that of the pietre verdi, or green rocks, and is 

 especially the zone of the triclinic feldspars, like those of the diorite, 

 euphotide and apenninite. The granites themselves of this zone — and 

 I cite those of Elba^ of Baveno, of Mont Orfano, and of Alzo, etc. — 

 although characterized by the beauty of their crystals of orthoclase, 

 are rich in albite. I have cited apenninite, which will be new to 

 you, so that I give the following explanation. Our geologists have 

 long recognized in the Apennines of Savoy the presence of a great 

 body of protogine or protogine-like gneiss. This rock is composed 

 of quartz and feldspar, in nodules rather than in crystals, and of 

 chlorite. A rock of the same character has been recognized by 

 Giordano in the Grand Cervisa. Now the feldspar of this rock, 

 which in the Ligurian Apennines, as well as in the Pennine Alps, 

 occupies a large surface, is in part soda-hearing, and I have thought 

 best to distinguish it from the true protogine, the feldspar of which 

 is orthoclase, by the name of apenninite. 



"In a great many localities in the Alps we see the pietre verdi 

 resting against the central gneiss, but in others the same series is 

 found lying nearly horizontally thereon. In the latter case meteoric 

 agencies destroy this superimposed series, and thus extend more 

 and more the area of the ancient gneiss, already widely exposed. 

 Were the rocks of the pietre verdi zone thus made to disappear 

 from the Alps, the height of these in many places would be much 

 reduced (thus, for example, the Grand Cervisa and the Grivola are 

 formed of this zone) ; and when at last these rocks were destroyed, 

 we should find the region entirely occupied by the ancient gneiss. 

 In a word, the mass of the Alps is formed of the ancient or primitive 

 gneiss, here and there overlain by the rocks of the pietre verdi zone." 



[For illustration of these different relations two figures are given 

 in the letter, one of which is along the valley of Lanzo, showing the 

 stratified pietre verdi series resting at a considerable angle upon the 

 ancient gneiss (the stratification of which is not indicated), and over- 

 laid by more recent sediments. The other section, in the valley of 

 Chisone, represents the ancient gneiss overlaid by a stratum of 

 Iherzolite, one of serpentine, and one of diallagic euphotide, the 

 attitude of all three being nearly horizontal.] 



"The ancient gneiss is very poor in minerals, but includes a 

 limited number of other rocks, such as quartzite, amphibolite, and 

 crystalline limestone. The zone of the green rocks or pietre verdi, 

 on the contrary, is very rich in minerals, as well as in varieties of 

 rocks. Whence have come the minerals of this zone, since they 

 have not [apparently] traversed the gneiss? Whence the porphyries 

 and the granites of this same zone, which we nowhere find intersecting 

 the gneiss ? We must conclude — and direct observation of the 

 facts demonstrates it — that the masses, the veins, and the so-called 

 bedded veins in which the zone of the pietre verdi is so rich, are 



