TACONIC QUESTION IN GEOLOGY. iSl 



or original Taconic, and thie Upper Taconic or Cambrian. In 1867, J. B. Perry described the 

 Taconic system of Vermont as composed of three parts : 1. Lower, consisting of quartz- 

 ites, marbles and talcoid schists, the original or Lower Tacouic of Emmons ; 2 and 3. Mid- 

 dle and Upper, including the nncrystalline fossiliferoirs Scranton and Georgia slates, and 

 the overlying- Red Sand-roL-k, which he regarded as the equivalent of Potsdam. The suc- 

 ôeeding graywacke, constituting a great part of the Upper Taconic of Emmons, was by 

 Perry supposed to be separated by an unconformity from the Red Sand-rock, and he was 

 disposed to divide it from the Taconic and connect it with the Champlain division.^ 



§ 152. Still more recently Marcou has given us his own latest views of these rocks in 

 Vermont. The true or typical Taconic is, according to him, the Upper Taconic of Emmons, 

 and rests unconformably upon the Lower Taconic. This upper series he divides into four 

 parts, in ascending order, designated the St. Albans, G-eorgia, Phillipsburg and Scranton 

 groups. In these are found, besides the Primordial fauna, fossils of the second fauna 

 in included limestones, a fact which he explains as indicating centres of creation in which 

 the forms of the second fauna first made their appearance ; the whole of these being, ac- 

 cording to him, below the horizon of the Red Sand-rock, which he supposes to overlie, un- 

 conformably, the Upper Taconic.** That the forms of the second fauna, fou.nd in portions 

 of this region, belong to a lower horizon than the Potsdam, is in discordance alike with 

 with the facts of paleontology and of stratigraphy, and is opposed to the conclusions of all 

 other observers in that region, including alike Emmons, Logan and Perry. Marcou's con- 

 clusions would seem to be based on some of the frequent cases of inversion of strata, or of 

 dislocation and upthrow, to which we have elsewhere alluded, and which led Logan to 

 place the Levis limestone near Quebec at the base of his Quebec group, and to represent 

 the Taconic marbles of southern Vermont as passing below the crystalline schists of the 

 Grreen Mountain range. 



It should, howcA^er, here be said, at the same time, that in a disturbed region like 

 eastern Vermont, where areas of the higher rocks of the second fauna exist, and have prob- 

 ably at one time been more widely spread than now, it is not impossible that there may 

 be outliers of a sandstone of Oneida or Medina age, such as in Pennsylvania we have 

 described as overlying unconformably Lower Taconic rocks, and also that siich Silurian 

 sandstones may have been confounded with the older Cambrian or Potsdam sandstone, 

 and thus afford a seeming justification for the strange hypothesis advanced by Marcou, 

 that the whole of the Appalachian Cambrian in Vermont is older than the Potsdam 

 sandstone. The absence of these Silurian sandstones at the base of the oiitliers of Silu- 

 rian limestones at Montreal, at Hudson and elsewhere, as already noticed in § 147, 

 renders, however, their presence in Vermont less probable. 



§ 153. The studies of the last few years have thrown much light on the character of 

 the lower portions of the Cambrian in its development to the east and south-east of the 

 Adirondack area. It has been noticed that the Red Sand-rock, and its accompanying slates 

 and limestones near Burlington, Vermont, referred by Emmons to the Potsdam, but by 

 Adams, and W. B. Rogers to the Medina, and by Logan to the summit of the Hudson River 

 group, were subsequently by Billings called Lower Potsdam, to indicate that the fauna of 

 these rocks belongs to a somewhat lower horizon than the typical Potsdam of the New 



' The Red Saudrock of Vermont, etc., J. B. Perry ; Proc. Bos. Soo. Nat. Hist., 1867, vol. xi. 

 « Marcou, Bull. Soc. Géol. de France, 1880, (3) ix, pp. 18^6. 



