Trof. T. Sterry Sunt — Elements of Primary Geology. 499 



diabasio rock, with sericitic schists, quartzites, iron-ores, and more 

 rarely with limestones. This, which in concert with Dr. Henry 

 Hicks, I have called Arvonian, is the Lower Huronian of C. H. 

 Hitchcock. 



IV. The Huronian, which in many regions rests unconformably 

 upon the Laurentian, or upon the Arvonian, constitutes the great 

 greenstone or Pietre-verdi group of the Alps, with its characteristic 

 eupho tides, serpentines and chrysolitic and amphibolic rocks. In this 

 series the intervention of sea-water is more evident than in the 

 preceding periods, perhaps for the reason that the sea had become 

 more magnesian from the results of the subaerial decay of erupted 

 plutonic masses, 



V. The great series of tender fine-grained gneisses passing into 

 granulites on the one hand and into quartzose mica-schists on the 

 other, makes what I called in 1871 the White Mountain or Montalban 

 series. This in many regions rests directly upon the Laurentian, 

 but it is believed in others to overlie chronologically the Huronian. 

 I say this with all deference to my honoured colleague, C. H. Hitch- 

 cock, who, recognizing the fact that the Arvonian and the Huronian 

 are wanting in many regions between the Laurentian and the 

 Montalban, and finding above the latter a series of schists which he 

 refers to the Huronian, maintains that the division is younger than 

 the Montalban. To this I would reply : First, that my observations 

 in the Alps, which are in accord with those of Von Hauer, Gastaldi, 

 and others, are to the effect that the true Pietre-verdi or Huronian 

 comes chronologically between the older and the younger gneisses, 

 which two divisions are there indistinguishable from the Laurentian 

 and Montalban respectively. Secondly, that the Taconian (or Lower 

 Taconic) series, which alike in the Alps and in North America 

 overlies the younger gneiss, has in portions a considerable litho- 

 logical resemblance to parts of the Huronian, to which its schistose 

 portions are related in character, somewhat as portions of the younger 

 gneisses with mica-schists of the Montalban are to the lower or 

 Laurentian gneisses. Hence it was that Murray, Credner, and for 

 a long time the present writer (who gave the name of Huronian in 

 1855), confounded the Huronian and the Taconian on Lake Superior. 



VI. The great series with quartzites, crystalline marbles, and the 

 iron-bearing schists of that region which, in 1873, I called the 

 Animikie series, is, as I have elsewhere endeavoured to show, identical 

 with the Taconian, for which it was long ago claimed by Emmons, 

 and is distinct from the Huronian alike in geographical distribution 

 and in lithological characters. This Taconian series extends in 

 eastern North America from the Gulf of St. Lawrence to Alabama, 

 including not only quartzites and marbles, but siderite and limonite, 

 and much of the magnetite of Pennsylvania; where it embraces 

 alike the "Primal slates" and the so-called "Altered Auroral and 

 Matinal strata " of H. D. Eogers. It is also the Itacolumitic series 

 of Lieber, in the Carolinas, and constitutes, so far as known, the 

 youngest member of the great succession of crystalline schists. 

 While parts of the Taconian have thus been confounded with 



