J. D. Dana — Brief history of Taconic ideas. 421 



But along with the light from Vermont, doubts entered 

 through the reference of some of the fossils of the limestone to 

 the Upper Silurian and perhaps Devonian, and the use made of 

 the few fossils of the Quartz jte. The facts were partly righted 

 in 1862 by Mr. Billings, the paleontologist of Canada, who re- 

 viewed the Vermont Report in this Journal, and claimed that 

 "the evidence of the fossils furnishes no reasonable ground for 

 placing the formation above the Lower Silurian."* 



Accepting the stratigraphical sections in the Vermont Report 

 as teaching what they appear to teach, and recognizing the 

 Lower Silurian age of the fossils from the limestone, and accept- 

 ing also Barrande's confirmation of Emmons's decision as to the 

 Primordial relations of the "Black slate" trilobites, the general 

 bearing of the facts made known, during this epoch of progress 

 and drawbacks, could hardly be mistaken. 



At this time the first edition of the writer's Manual of Geol- 

 ogy f was published. The preface bears the date of the close 

 of the printing, November 1, 1862. The Potsdam period in 

 American Geology had already become expanded into the 

 Primordial by the discovery, six years before, near Boston, of 

 specimens of Paradoxides Harlani% and by facts received 

 from abroad ; and it is designated in the work (pp. 169, 

 171) the "Potsdam oh Primordial Period," and made 

 the equivalent of the era of the Paradoxides and other 

 Primordial beds of Scandinavia and Bohemia, as well as of that 

 of the Lingula Flags and underlying Cambrian of Great Britain. 

 Moreover, Paradoxides, Olenus, and other Lower Cambrian 

 genera are cited, and P. Ilarlani appears among the figured 

 species. Barrande's determinations of the Georgia Slate Trilo- 

 bites, making them and the beds containing them Primordial, 

 are recognized by mentioning the beds and fossils among the 

 facts of the "Potsdam or Primordial Period" — conforming in 

 this to the decision of Emmons as well as Barrande. 



The Vermont discoveries of fossils in the Eolian limestone 

 had proved that the limestone and the overlying slates were 



*E. Billings, this J., II., xxxiii, 416, 1862. 



In 1870 the chief divisions in the geology of Vermont were briefly stated by 

 Prof. C. H. Hitchcock in a folio of six pages bearing the date of March 1st. His 

 further study of the State, in connection with the work of the Canadian Survey, 

 had led him to refer at this time the Kolian or Stockbridge limestone and associa- 

 ted slates to the Quebec group, and the Quartzyte, Red Sandrock and the Georgia 

 slates and T31ack slate to the Potsdam or Primordial, the last-mentioned the oldest. 



f Manual of Geology by James D. Dana, 798 pp. 8vo, illustrated by a chart of 

 the world and over 2000 figures. Philadelphia, 1863. 



% W. B. Rogers, this J., II, xxii, 296, 1856, from a letter to J. D. Dana of August 

 13. Prof. Rogers compares the fossil with the P. spinosus of Barrande, and identi- 

 fies it with the P. Harlani of Green. Mr. Green's cast of a specimen of unknown 

 locality, had been widely distributed, and had reached Barrande. He also shows 

 by Green's description of the rock, that his specimen was probably of the same 

 locality. 



