470 



THE AZOIC SYSTEM AND ITS SUBDIVISIONS. 



the two can for a moment confound them. Prof. Eogers is therefore obliged 

 to assume a new series of crystalline rocks, distinct from Loth the Laurentian 

 and Huronian systems, hut undistinguishable from the altered palaeozoic series, 

 or else to admit that the whole of his gneissic series in Pennsylvania is, like 

 the corresponding rocks in Canada, of paleozoic age." 



In the Presidential Address of Dr. Hunt before the American Asso- 

 ciation, 1871, it is stated that Prof. H. D. Rogers has distinguished 

 three districts in Pennsylvania of various cryBtalline schiyts, which, in 

 his Eeport on the geology of that State, he included under the name of 

 Gneissic or Hypozoic rocks. The gneiss of the northern or South Moun- 

 tain belt is said by Dr. Hunt to be '* lithologically as well as geognosti- 

 cally identical with that of the Highlands, and belongs like it to the 

 Adirondack or Laurentian system of crystalline rocks." The gneiss of 

 the middle district seems to be regarded as Laurentian, while that of 

 the third or southern district is referred to the White Mountain series, 

 with the exception of the middle subdivision, which is said to present 

 the aspect of the second or Green Mountain series. 



Professor Rogers is stated to have placed above the hypozoic gneisses 

 his azoic or semi-metamorphic series, which Dr. Hunt regards as belong- 

 ing to the Green Mountain or Huronian series, in regard to which he 

 remarks as follows : — 



" The azoic 'or so-called metamorphic primal strata are said to have a very 

 uniform, nearly vertical, dip, or with high angles to the southward, while the 

 micaceous and gneissic strata of the northern subdivision of the southern dis- 

 trict of so-called hypozoic rocks, limiting these last to the south, present either 

 minute local contortions or wide gentle undulations, with comparatively mod- 

 erate dips, for the most part to the northward. From this, I think we mny 

 infer that the nearly vertical strata must be, in truth, older underlying rocks, 

 belonging, not to the pahxiozoic system, but to our second series of crystalline 

 schists." (Proc. Am. Assoc. Adv. Sci., 1871, XX., pp. 7-9.) 



It seems, although we were, in 18G1, emphatically informed that the 

 *' lithological and diemical characters of the Appalachian gneiss are so 

 totally distinct from the crystalline strata of the Laurentian system, .... 

 that no one who has studied the two can for a moment confound them;' that 

 now we are as positively told that part of it is ''lithologically as well as 

 geognostically identical with .... [the] Laurentian system of crystalline 



roch.'^ 



In 1875 Prof. J. P. Lesley stated that the Huronian or Green Moun- 

 tain series seems to overlie the White Mountain series in the vicinity of 

 Philadelphia; also, that the conglomerate beds of the Primal scries hold 



