Br. T. Sterry Hunt — On Italian Geology. 537 



regions in whicli the pietre verdi series plays an important part 

 becomes easy to understand ; but it is, on the contrary, extremely 

 complicated if we consider the rocks of this series as intrusive. In 

 a great many parts of the Alps we see these rocks rising into con- 

 siderable elevations, as in Monte Viso ; elsewhere again they are 

 overlain by the anthracitic series, by the Trias, or by still more recent 

 terranes. Thus in the valleys of the Bormida, and the Erro, and in 

 other valleys of the Ligurian Apennines, they are directly covered 

 by the Miocene ; and again, as in the Apennines of Bologna, of 

 Florence, etc., are overlain by the Eocene or the Upper Cretaceous. 

 The separation of the two chains, Apennine and Alpine, is but a 

 geographical fiction ; it would be absurd to attempt to separate them 

 geologically. I have visited the valleys and the depressions along 

 which geographers have drawn the lines of separation, and have 

 there found nothing but Alpine rocks, serpentine, apenninite, calc- 

 schists, etc. ... 



" To-morrow I leave for the Maritime Alps, where I shall remain 

 for about a month in order to visit the valleys of the Macra and the 

 Stura, that of Geno and that of the Vermagna, making for the thii-d 

 time this journey, which is a weary and a painful one, especially for 

 the valley of the Macra, where one is forced to undergo many 

 pri\'ations. I am delighted to think that our literary correspondence 

 is renewed, and regret very much that circumstances deprive me of 

 the pleasure of being with you at the Congress in Paris. . . . 



" Affectionately yours, 

 '' To Mr. T. Sterry Hunt. B. Gastaldi." 



As regards the pietre verdi series, of which he has here so well set 

 forth the importance, I have in the volume already quoted (Mineral 

 Physiology and Physiography) shown that Gastaldi not unfrequently 

 employed it, as in the foregoing letter, to designate the whole suc- 

 cession of crystalline schists above the ancient or central gneiss — - 

 speaking of these collectively as the "newer crystalline series." This 

 howevei', includes a great body of younger gneiss and mica-schists 

 above the group characterized by serpentine, euphotide, diorite, etc., 

 which he has here so clearly defined as resting upon tlie ancient 

 gneiss. Neri, in his sections in north-western Italy, distinguishes 

 above the ophiolitic or pietre verdi horizon, a group of mica-schists 

 with granites, while Gerlach described the same as recent gneiss 

 and granite, followed by gneissic mica-schists. Gastaldi himself, 

 in more detailed accounts, used the term pietre verdi in the same 

 restricted sense as Neri. Thus in 1874: [Stuclii geologici sxdli Alpi 

 cccidentale, part 2) he speaks of " the pietre verdi properly so-called," 

 and declares it to be comprised between " the ancient porphyroid and 

 fundamental gneiss," and "the recent gneiss, which latter is finer- 

 grained and more quartzose than the other." He elsewhere in this 

 same memoir speaks of this higher portion of the " newer crj'stalline 

 series " (oftentimes, as in the above letter, comprehended in his 

 "pietre verdi zone") as a mica-schist, — a gneissic mica-schist, — as 

 recent gneiss and mica-schist, — and also. as a very micaceous gneiss, 

 often passing into mica-schist and sometimes hornblendic. He says 



