No. 4.] HUNT — ON CAMBRIAN AND SILURIAN. 441 



which connect this fauna with that of the succeeding Lower 

 Devonian or Erian period. To this Lower Helderberg horizon 

 (corresponding to the Ludlow of England) appear to belong 

 certain fossiliferous beds found along the Atlantic coast of Maine 

 and of New Brunswick, in Nova Scotia and (?) in Newfound- 

 land ; as well as others included in the Appalachian belt in 

 Massachusetts, New Harapshire, Vermont and Quebec, along the 

 Connecticut valley and its north-eastern prolongation. The fos- 

 siliferous strata just noticed, both in the Connecticut valley, and 

 along the Atlantic coast, occur in small areas among the older 

 crystalline schists, often made up of the ruins of these, and in 

 highly inclined attitudes. The same is true in some places of 

 the similarly situated strata of Cambrian, Devonian and Lower 

 Carboniferous periods. These derived strata, of different ages, 

 have, from their lithological resemblances to the parent rocks, 

 been looked upon as examples of a subsequent alteration of 

 paleozoic sediments; and by a farther extension of this notion, 

 the pre-Cambrian crystalline schists themselves throughout this 

 region have been looked upon as the result of an epigenic change 

 of these various paleozoic 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 partial 

 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 (appar- 

 ently 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 conglo- 

 merate, and of the succeeding formations up to the Lower 

 Helderberg division. This latter, in various localities in the 

 valleys of the Hudson and the St, Lawrence, rests unconformably 

 upon the strata of the second 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 conglo- 



