'^^-_ 



PENNSYLVANIA. 



469 



that "a debt of gratitude is due Dr. Hunt for his hif^torical monograph," 

 although admitting that " no final demonstration has been accomphshed 

 by the author [Dr. Hunt] of those problems of superposition, uncon- 

 formability, and idontilication, at which so many geologists are still 

 half despairingly at work." (Azoic Rocks, p. vii.) Perhaps this ad- 

 mitted want of success will not be so difficult to account for. when one 

 takes into consideration Some of the views published by Di*. fiuat pre- 

 vious to his engagement on the Pennsylvania Survey. 



In 18G1, Dr. Hunt remarked, regarding the Hypo^oic or Gneissio 

 series of Professor Rogers (Am. Jour. Sci., 1861, (2) XXXI., pp. 394, 

 395) : 



" We have along the great Appalachian chain, from Georgia to the Gulf of 

 St. Lawrence, a third series of crysiulliiic strata, which form the giicissoid and 

 mica slate series of most American geologists, the hypozoic group of Prof. 

 Rogers, consisting of feldspathic gneiss, with quart^iites, argillites, micaceous, 

 epidotic, chloritic, t^lcose and specular schists, accompanied with steatite, dio- 

 rites and chromifcroua ophiolites. This group of strata has been recognized by 

 Sallbrd in Tennessee, by Rogers in Pennsylvania, and by most of the New 

 England geologists as forming the base of Appalachian system, while Sir 

 William Logan, Mr. Hall, and the present writer have Ilov many years main- 

 tained that they are really altered palaeozoic sediments, and superior to the 

 lowest fossiliferous strata of the Silurian series. Sir William Logan has 

 shown that the glieissoid ranges in Eastern Canada have the form of syncli- 

 nals, and are underlaid by shales which exhibit fossils in their prolongation, 

 while his sectii>n3 leave no doubt tiiat these ranges of gneiss, with micaceous^ 

 chloritic, talcose and specular schists^ epidosites, quartzitesy diorites and ophio^ 

 litcs, are really the altered sediments of the Quebec group, which is a lower 

 member of the Silurian series, corresponding to the Calciferous and Chazy 

 formations of New York, or to the Primal and Auroral series of PennsylvaniiU 

 Prof. Rogers indeed admits that these are in some parts of Pennsylvania 

 metamorphosed into feldspathic, micaceous and talcose rocks, which it is ex- 

 tremely dillicult to distinguish from the hypozoic gneiss, which latter, how- 

 ever, he conceives to present a want of conformity with the pala30zoic strata. 

 To this notion of the existence of two groups of crystalline rocks similar in 

 lithalogical character but different in age, we have to object that the hypozoic 

 gneiss is identical with the Green Mountain gneiss, not only in lithological 

 character, l)ut in the preserice of certain rare metals, such as chrome, titanium, 

 and nickel which characterize its magncsian rocks ; all of these we have shown 

 to be present in the unaltered sediments of the Quebec group, with which Sir 

 William Logan has identified the gneiss formation in question. Besides 

 which the lithological and chemical characters of the Appalachian gneiss are 

 so totally distinct from the crystalline strata of the Laurcntian system, with 

 which Prof. Rogers would seem to identify them, that no one who has studied 



