on American Geology, 83 



Overlying the Laurentian series on Lake Huron and Superior, 

 we have the Huronian system, about 10,000 feet in thickness, 

 and consisting to a great extent of quartzites, often conglomerate, 

 with limestones, peculiar slaty rocks, and great beds of 

 diorite, which we are disposed to regard as altered sediments. 

 These constitute the lower copper-bearing rocks of the lake 

 region, and the immense beds of iron ore at Marquette and other 

 places on the south shore of Lake Superior have lately been found 

 by Mr. Murray to belong to this series, which is entirely wanting 

 along the farther eastern outcrop of the Laurentian system. This 

 Huronian series appears to be the equivalent of the Cambrian 

 sandstones and conglomerates described by Murchison, which form 

 mountain masses along the western coast of Scotland, where they 

 repose in detached portions upon the Laurentian series. 



Besides these systems of crystalline rocks, the latter of which 

 is local and restricted in its distribution, we have along the great 

 Appalachian chain, from Georgia to the Gulf of St. Lawrence, a 

 third series of crystalline strata, which form the gneissoid and mica 

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

 Rogers, consisting of feldspathic gneiss, with quartzites, argillites, 

 micaceous, epidotic, chloritic, talcose and specular schists, 

 accompanied with steatite, diorites and chromiferous ophiolites. 

 This group of strata has been recognized by Safford 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 for many 

 years maintained 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 gneissoid ranges in Eastern 

 Canada have the form of synclinals, and are underlaid by shales 

 which exhibit fossils in their prolongation, while his sections leave 

 no doubt that these ranges of gneiss, with micaceous, chloritic, 

 talcose and specular schists, epidosites, quartzites, diorites 

 and ophiolites, 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 Pennsylvania. Prof. Rogers indeed admits 

 that these are in some parts of Pennsylvania metamorphosed into 

 feldspathic, micaceous and talcose rocks, which it is extremely diffi- 

 cult to distinguish from the hypozoic gneiss, which latter, however, 

 he conceives to present a want of conformity with the palaeozoic 

 strata. 



