walcott.] RED SANDROCK. 97 



Survey of Vermont the occurrence of roofing slates in southern Ver- 

 mont l which he refers to the Taconic slate of Dr. Emmons, without a 

 further attempt to assign them to a geologic horizon. 



In the following year a section is given of Snake Mountain by Prof. 

 Adams * in which the Red sandrock is shown resting conformably upon 

 the Hudson Eiver shale. In 1847 he referred to his studies of the Red 

 sandrock 3 and noticed the discovery of fragments of trilobites which 

 Prof. James Hall identified as Oonocephalus. 4 He next assigned his 

 Red Sandrock to the Upper Silurian, correlating it with the Medina 

 sandstone. 5 Dr. E. Emmons criticised this view of Adams, and stated 

 that he was in error. He regarded the formation as of Calciferous or of 

 Potsdam age as proved by the fossils, stating that the rocks rest on the 

 Taconic slate. 6 Prof. Adams reasserted his view in 1848, 7 stating that no 

 line of fracture occurred above the Trenton limestone,and that the Snake 

 Mountain section showed that it contained Utica and Hudson River 

 rocks. Later, Dr. Zadock Thompson adopted the view that the Red 

 sandrock was in its natural position on the summit of Snake Mountain. 8 

 The view that the Red sandrock series was the equivalent or the Me- 

 dina of the New York section was sustained by Prof. W. B. Rogers 9 

 and the Medina or Clinton age of the " Red sandrock" was supported 

 by the Geological Survey of Vermont. 10 



Mr. E. Billings, on learning of the discovery of fossils in the " Red 

 sandrock" near Swanton, Vermont, by Dr. G. M. Hall and Rev. J. D. 

 Perry, visited the locality and found a small Theca and a Oouocepha- 

 lites. Upon this paleontological evidence he referred the strata to about 

 the horizon of the Potsdam sandstone, to which position it Las since 

 been assigned by most authors who have had occasion to mention it. 11 

 Mr. Billings also corrected the statement of Prof. Hall, that the trilo- 

 bites of the Georgia slate were from the Hudson terrane, and referred 

 them to the Primordial or Lower Potsdam. This transferred the Geor- 

 gia series and the associated " Red sandrock w to the Cambrian. 12 



I have thus far referred only to the " Red sandrock," as it was men- 

 tioned more definitely, and assigned to a geological position prior to 

 the argillaceous and arenaceous shales and slates that overlie it. As 

 the "Red sandrock" and these shales or slates will be spoken of together 



1 First Annual Keport on the Geology of Vermont. Burlington, 1845, p. 35. 



* Second Annual Report on the Geology of the State of Vermont. Burlingtou, 1846. p. 163. 



3 Third Annual Report on the Geology of the State of Vermont. Burlington, 1847, pp. 13-15. 



4 Letter on certain fossils in the Red sandrock of Higligate. Third Anuual Report on the Geology of 

 the State of Vermont. Burlington, 1847, p. 31. 



s On the Taconic System. Am. Jour. Agric. and Sci., vol. 6,1817, p. 260. 

 '(On the Taconic System.) Am. Jour. Agric. and Sci., vol. 6, 1847, p. 260. 

 7 On the Taconic Rocks. Am. Jour. Sci., 2d ser., vol. 5, 1818, pp. 108-110. 

 •Geology of Vermont. Nat. Hist, of Vermont, Burlington, 1853, Appendix, p. 45. 



9 (Notes on the geological structure of western Vermont.) Report on the Geology of Vermont, vol. 

 1, 1861, pp. 326, 327. 



10 Hitchcock, C. H. Report on the geology of Vermont. Notes on the sections, vol. 2, 1861, p. 650. 

 "On the age of the red sandstone formation of Vermont. A m. Jour. Sci., 2d ser., vol. 32, 1861, p. 232. 

 "OuProf. J. Halls claim to priority in the determination of the age of the rod sandrock series of 



Vermont, Am. Jour. Sci., 'J«l ser., vol. 3'J, 1862, pp. 370-376- 



Bull. 81 7 



