Dr. T. Sterry Hunt — On Italian Qeology. 53& 



whole indistinguisliable from the Laurentian of North America, and 

 also the characteristic serpentinic or proper pietre verdi group over- 

 lying it, I found the recent gneiss and mica-schist series apparently 

 overlying transversely both of these, and seemingly identical with 

 the Montalban or younger gneissic series of the White Mountains 

 and of Philadelphia in North America. An absence of the ophiolitic 

 or true pietre verdi group between the older and the younger gneissic 

 series, which is apparent elsewhere in the Alps, and in many places 

 in North America, may be due either to non-deposition or to erosion. 

 The existence of conglomerates holding rolled pebbles in the younger 

 gneissic series, both in Europe and America, shows erosion to have 

 played an important part in Arch^an as in later times, and is in 

 harmony with the observed stratigraphical discordances in the 

 crystalline rocks, each one of the upper divisions in turn being found 

 to rest upon the ancient gneiss. 



The younger gneissic or Montalban series I have found well dis- 

 played in Mont St. Gothard and in the Ticino basin in Switzerland. 

 To it also apparently belong the granulite rocks and the mica-schists 

 of the Mittelgebirge in Saxony, with their dichroite- gneiss, Iherzolite, 

 and gai-netiferous serpentine, and also the micaceous gneisses of the 

 Erzgebirge, with their included limestones and amphibolic rocks, and 

 their overlying mica-schists. In these latter are found the remark- 

 able conglomerate beds described by Hauer in 1879, the pebbles of 

 which are apparently derived from the ancient or central gneiss, of 

 which they have the characters.^ 



While thus referring the younger gneisses and mica-schists alike 

 of Saxony and of the Alps to the Montalban, I have maintained that 

 the uppermost division of the newer crystalline series of Gastaldi is 

 to be regarded as the equivalent of the Taconian or Lower Taconic 

 of North America, designated by Lieber the Itacolumitic series ; a 

 great group of strata which is traced from the Gulf of St. Lawrence, 

 with some interruptions, nearly to the Gulf of Mexico, and westward 

 to the basin of Lake Superior and beyond. This series should be 

 carefully distinguished from the Upper Taconic, a younger uncrystal- 

 line series, different in geographical distribution, and containing a 

 well-defined Cambrian fauna. The Taconian or Lower Taconic, 

 whose real stratigraphical relations were already clearly defined 

 more than fifty years ago by Amos Eaton, has since, by various 

 theorists of the metamorphic school, been alternately regarded as 

 altered Cambrian, altered Ordovician, altered Silurian, altered Car- 

 boniferous, and in part even as altered Triassic;- a history which 

 recalls that of the similar strata of the Apuan Alps, including the 

 marbles of Carrara and Massa, which have by different writers been 



1 See for a detailed discussion of the questions here involved, the author's " Mineral 

 Physiology and Physiography," on The Geology of the Alps and the Apennines, pp. 

 457-482 ; The Serpentines 'of Italy, pp. 482-496 ; and further, The Metamorphia 

 Hypothesis, pp. 654-673. 



2 For a detailed account of the Taconic controversy see the author's "Mineral 

 Physiology and Physiography," 617-686; also, more concisely and with new facts, 

 " The Taconic Question Restated," Amer. Naturalist, Feh. Mar. and Apl. 1887. 



