416 CAMBRIAN AND SILURIAN IN NORTH AMERICA. [XV. 



throughout this region have been looked upon as the result of 

 an epigenic change of these various palaeozoic strata ; portions 

 of which, here and there, were supposed to have escaped 

 conversion, and to have retained more or less perfectly their 

 sedimentary character, and their organic remains, elsewhere 

 obliterated. 



From the absence of the second fauna we may conclude that 

 the great Appalachian area was, at least in New England and 

 Canada, above the ocean during its period, and suffered a par- 

 tial and gradual submergence in the time of the third fauna. 

 This movement corresponds to the well-marked paleontological 

 and stratigraphical break between the second and third faunas 

 in the great continental basin to the westward, made evident 

 by the appearance of the Oneida or Shawangunk conglomerate 

 (apparently derived from the ruins of Lower Cambrian rocks) 

 which, in some parts, overlies the strata of the Hudson River 

 group. The break is elsewhere shown by the absence of this 

 conglomerate, and of the succeeding formations up to the 

 Lower Helderberg division. This latter, in the valley of the 

 St. Lawrence, rests unconformably upon the strata of the sec- 

 ond fauna, as it does upon the older crystalline rocks to the 

 eastward. 



In Ohio, according to Newberry, the base of the rocks of the 

 third fauna (Clinton and Medina) is represented by a conglom.T 

 erate which holds in its pebbles the organic remains of the 

 underlying strata of the second fauna. 



To the northeastward the island of Anticosti in the Gulf of 

 St. Lawrence presents a succession of about 1,400 feet of cal- 

 careous strata rich in organic remains, which, according to Mr. 

 Billings, include the species of the Medina, Clinton, and Niag- 

 ara formations, and were named by him, in 1857, the Anticosti 

 group. They rest upon nearly 1,000 feet of almost horizontal 

 strata, consisting of limestones and shales rich in organic re- 

 mains, with many included beds of limestone-conglomerate. 

 This lower series has by the geological survey of Canada been 

 referred to the Hudson River group ; but, notwithstanding the 

 large number of forms of the second fauna which it contains, 



