•540 Dr. T. Sterry Hunt — On Italian Geology. 



referred to various horizons from Cretaceous down to pre-Palseozoic, 

 at which latter they are placed by Gastaldi, in the upper part of his 

 "newer crystalline series," as also by Jervis in the second volume of 

 his valuable treatise, I Tesoro Sotteranei delV Italia. 



This Taconian or newest crystalline group embraces in North 

 America besides quartzites (sometimes in flexible elastic layers) and 

 crystalline limestones affording both banded and statuary marbles, 

 large deposits of iron-ores, alike magnetite, hgematite, and limonite, 

 the latter being formed by epigenesis, in some cases from pyrites and 

 in others from siderite. It also includes a great mass of argillites, 

 and of soft unctuous schists, often described as talcose, and though 

 more generally sericitic, sometimes containing chlorite and talc, 

 together with occasional amphibolic and feldspathic rocks, massive 

 serpentines and ophicalcites, and bearing throughout a marked 

 resemblance to the upper division of the newer crystalliae series of 

 the Alps. 



As the writer has elsewhere pointed out, the chemical and 

 mineralogical conditions of the underlying pietre verdi horizon 

 were repeated, though with diminished intensity, at this later time 

 in the history of the newer crystalline series, producing in the 

 younger rocks thereof such resemblances to the older that the 

 Taconian strata were not unnaturally confounded with the Huronian. 

 Thus, to the south of Lake Superioi', Emmons having in 1846 

 recognized the Taconian, he was led, when the Huronian was 

 announced in 1855, to maintain (in an unpublished paper) that it 

 was in no way distinct from his Lower Taconic. On the other 

 hand, the present writer, in common with Murray, Credner, and 

 others, included these same Taconic rocks in that region with the 

 Huronian, and it was not until after a prolonged study of the 

 Taconian in the more eastern regions of North America, that he was 

 enabled to show that the two series had really been included in the 

 Huronian as defined in the vicinity of Lakes Superior and Huron ; 

 where also the recent gneisses and mica-schists are met with, as well 

 as the ancient or primitive granitoid gneiss. In like manner, as we 

 have seen, Gastaldi was led, from such lithological likenesses, to 

 include the upper and lower division of his newer crystalline series, 

 with their intervening, recent gneisses and mica-schists, under the 

 comprehensive name of the pietre verdi zone. These partial resem- 

 blances between the crystalline rocks of succeeding divisions serve 

 to illustrate the different stages in the process of evolution of the 

 crystalline rocks in successive ages by chemical agencies from an 

 originally undifferentiated mineral matter, as I have endeavoured to 

 set forth in a recent paper on " The Elements of Primary Geology." ^ 



^ Geological Magazine, November, 1887. 



