262 GEOGNOSY OF THE APPALACHIANS. [XIII. 



of Nebraska, accordiDg to Hayden, the only representative of 

 these lower formations is about one hundred feet of sandstone 

 holding Potsdam fossils.* 



In striking contrast to this, it has been shown that along the 

 Appalachian range from Newfoundland to Tennessee these 

 lower formations are represented by from 8,000 to 15,000 feet 

 of fossiliferous sediments. It has been suggested by Logan 

 that these widely differing conditions represent deep-sea accu- 

 mulations on the one hand, and the deposits from a shallow 

 sea which covered a submerged continental plateau on the 

 other ; the sediments in the two areas being characterized by a 

 similar fauna, though differing greatly in lithological characters 

 and in thickness. To this we may add, that the continental 

 area, being probably submerged and elevated at intervals, be- 

 came overlaid with beds which represent only in a partial and 

 imperfect manner the great succession of strata which were 

 being accumulated in the adjacent ocean, t 



In a paper which I hope to present to the geological section 

 during the present meeting of the Association, it will be shown, 

 from a study of the rocks of the Ottawa basin, that the typical 

 Champlain division not only presents important paleontological 

 breaks, but evidences of stratigraphical discordance at more 



* American Journal of Science (2), XXV. 439; XXXI. 234. [Later obser- 

 vations show great variations in the thickness of these lower rocks in the West. 

 In the Wahsatch Mountains are found, according to Bradley, from 1,500 to 

 2,000 feet of sandstones and conglomerates, regarded as Potsdam, overlaid by 

 3,000 feet of magnesian limestones and shales, holding fossils of th 

 and, towards the summit, of Niagara and probably of Lower Helderberg 

 age ; the whole followed by 2,000 feet of Devonian sandstones and 3,000 

 feet of Carboniferous limestones. In the Teton Mountains, however, accord- 

 ing to the same observer, this great thickness of Potsdam and Levis rocks is 

 represented by only 700 feet of quartzites and limestones, overlaid by about 

 600 feet of magnesian limestones, probably of Niagara age, followed by 2,000 

 feet of Carboniferous limestones. In the Wind River Mountains, in western 

 Wyoming, Professor Comstock has described a remarkable series, including 

 Potsdam and Levis, followed by strata of Oriskany age, Carboniferous lime- 

 stones, Triassic, Jurassic, and Cretaceous rocks, all apparently conformable, 

 and resting at an angle of about 20 on the crystalline Eozoic rocks. Re- 

 mains of the fauna of the Trenton period (Upper Cambrian) have moreover 

 very recently been made known to us from the West.] 



t Ibid. (2), XLVI. 225. 



