GEOLOGY. 293 



them the same view. James Giekie, from his previous stud- 

 ies of the latter region, had regarded the whole series as 

 one of altered sediments. The serpentines of both of these 

 regions resemble those of the American Huronian, and the 

 similar ones of Ansrlesea which are included in the Huronian 

 (Pebidian) series. When it is considered that there is abun- 

 dant evidence that the North American serpentines are in- 

 digenous, though often, like deposits of gypsum and of iron 

 ores, in lenticular masses ; and, further, that the movements 

 which the ancient strata have suffered have produced great 

 crushings and displacements, it is not difficult to understand 

 the deceptive appearance of intrusion which these rocks of- 

 ten exhibit, and which are scarcely more remarkable than 

 the accidents presented by coal-seams in some disturbed and 



contorted areas. 



WISCONSIN. 



The pre-Cambrian rocks of Wisconsin (noticed in the Rec- 

 ord for 1877) have been further examined by Irving, and 

 chiefly as they occur to the south of the great Primary or 

 pre-Cambrian area of the region, where they appear rising 

 through the horizontal Cambrian (Potsdam) sandstone, " pro- 

 truding, but not intruded." They are described as consist- 

 ing in large part of quartzites, massive and vitreous, or slaty 

 and interlaminated with soft so-called talcose schists. These 

 rocks the Lower Potsdam of Alex. Winchell and the al- 

 tered Potsdam of Percival were long since, by James Hall, 

 regarded as Huronian, a view which is adopted by Irving. 

 With them is found a great development of the halleflinta 

 or petrosilex-porphyry, which is found conformably succeed- 

 ing the quartzites, in beds with a high northern dip, and in 

 parts becomes schistose, or is interstratified with soft schists. 

 In one section the petrosilex beds measure 3200 feet ; while 

 another section of 5000 feet, chiefly of quartzites and schists, 

 shows 600 feet of the petrosilex. Irving, who has studied 

 these petrosilexes both chemically and microscopically, fol- 

 lows Hunt in referring them to the Huronian series. They 

 should probably be included in the newly proposed Arvonian 



series of Hicks. 



THE BLUE RIDGE. 



Bradley has further set forth his views as to the supposed 

 Paleozoic age of the crystalline rocks of the Blue Ridge in 



