108 THE CAMBRIAN. Tbuli. 81. 



Dr. T. S. Hunt, in 187S, 1 gives an historical review of tbe rocks re- 

 ferred to the Cambrian and Taconic systems and in this ^ay speaks of 

 the " Upper Taconic" and refers it to the Cambrian, and the "Granu- 

 lar Quartz w to an Archean system. Again, in 1883,-'84,-'8G, he went 

 over the same ground, 2 but did not add any original information upon 

 the subject. He adopted the view of Prof. Eaton so well expressed in 

 the section of 1824, and brought down to 1886 the erroneous view of the 

 unconformity between the Calciferons sandrock and the Argillite. To 

 the strata which Dr. Emmons included in the Taconic system, in 1842, 

 he gave the name Taconian, referring them to a pre-Cambrian, Archean, 

 group of rocks. 



In a paper upon the colonies in the Taconic rocks of the borders of 

 Lake Champlain, 3 Brof. Jules Marcou gives a resum6 of his investiga- 

 tions in northern Vermont up to date. In the vertical section accom- 

 panying the geological map, the Potsdam sandstone is placed at the 

 summit of the upper Taconic series, and then in order below, the Swan- 

 ton schists, Phillipsburg group, Georgia schists, and the St. Albans 

 group. On sections in the text the Potsdam sandstone is represented 

 as unconformably superjacent to the Georgia slates, the Phillipsburg 

 group, and the Swanton schists, and the St. Albans group. A general 

 description is given of the formations as interpreted by Prof. Marcou. 

 As now known the Potsdam sandstone as identified by him, is the Red 

 sandrock of the Vermont geologists, or the arenaceous magnesian lime- 

 stone of Logan. Its strati graphical position is at the base of the series 

 described, or at the base of the Lower Cambrian as now understood. 



A series of geological sections across Vermont and New Hampshire 



by Prof. C. H. Hitchcock 4 have the Red Sandrock series marked as 



Potsdam and the Georgia slate series as Cambrian. The Granular 



Quartz of the southern portion of Vermont is all marked Potsdam. In 



the text 5 Prof. Hitchcock says : 



Three bands of sandstone therefore are referred to the Potsdam in the Champlain 

 valley : first, the normal gray sedimentary beds at the foot of the Adirondack^, 

 always known under this name since 1840 ; second, the quartzite on the tlauk of the 

 Green Mountains; third, a range of red sandstone and dolomite from the Canada 

 line to Bridport, where it is succeeded by outcrops of a material not distinguish- 

 able from the first named band. Partly accompanying the middle band is a series of 

 slates and hard sandstones, passing into roofing. slates- called the Georgia group in 

 the State report, which carries such fossils as Olenellus and Angelina, and is, there- 

 fore, thought to be somewhat older than the typical Potsdam sandstone. 



In the same publication Prof. E. P. Whitfield 6 states it to be his 



1 Special report on the trap dikes and azoic rocks of southern Pennsylvania, 2d Geol. Surv. Pa., E., 

 1878, p. 253. 



2 The Taconic question in geology. Mineral Physiology and Physiography. A second series of 

 chemical and geological essays, with a general introduction. 1886, pp. 517-686. 



3 Sur les colonies dans les roches taconiques des hords du lac Champlain. Soc. geol. France, Ball., 

 3 me ser, vol. 9, 1880, pp. 18-46. 



4 Geological sections across Vermont and New Hampshire. Am. Mus. Nat. Hist., Bull., vol. 1, 1884, 

 pp. 155-179. 



&Op.cit,,p. 160. 



•Notice of some new species of Primordial fossils in the collections of the Museum, and correction* 

 of previously described species. Am. Mus. Nat. Hist.. Bull., vol. 1, 1884, p. 140. 



