260 GEOGNOSY OF THE APPALACHIANS. [XIII. 



the neighborhood of Quebec, and, without the evidence of 

 fossils, every one would be authorized to deny it." * 



The rocks from western Vermont, which had furnished to 

 Hall the species of Olenellus, have long been known as the 

 Red sand-rock, and, as we have seen, were by Emmons, in 1 842, 

 referred to the age of the Medina sandstone, a view which 

 the late Professor Adams still maintained as late as 1847. t In 

 the mean time Emmons had, in 1855, declared this rock to 

 represent the Calciferous and Potsdam formations, the brown 

 sandstones of Burlington and Charlotte, Vermont, being re- 

 ferred to the latter. J This conclusion was confirmed by 

 Billings, who, in 1861, after visiting the region and examin- 

 ing the organic remains of the Red sand-rock, assigned to it a 

 position near the horizon of the Potsdam. Certain trilobites 

 found in this Red sand-rock by Adams, in 1847, were by Hall 

 recognized as belonging to the European genus Conocephalus 

 (= Conocephalites and Conocoryphe), whose geological horizon 

 was then undetermined. || The formation in question consists 

 in great part of a red or mottled granular dolomite, associated 

 with beds of fucoidal sandstone, conglomerates, and slates. 

 These rocks were carefully examined by Logan in Swanton, 

 Vermont, where, according to him, they have a thickness of 

 2,200 feet, and include toward their base a mass of dark- 

 colored shales holding Olenellus with Conocephalites, Obolella, 

 etc. ; Conocephalites Teucer, Billings, being common to the 

 shales and the red sandy beds.1T Many of these fossils are 

 also found at Troy and at Bald Mountain, New York, where 

 they accompany the At ops of Emmons, now recognized by 

 Billings as a species of Conocephalites. 



* Logan's letter to Barrande, American Journal of Science (2), XXXI. 218. 

 The true date of this letter was December 31, 1860, but, by a misprint, it is 

 made 1831. 



+ Adams, American Journal of Science (2), V. 108. 



% Emmons, American Geology, II. 128. 



American Journal of Science (2), XXXII. 232. 



II Ibid. (2), XXXIII. 374. 



II Geology of Canada, 1863, p. 281 j American Journal of Science (2), 

 XLVI. 224. 



