BIGSBY PALAEOZOIC BASIN OF NEW YORK. 447 



of the Appalachian basin, whether we measure it by the smallness 

 in the proportion of the species which bridge the gulf, or by the 

 alteration in their types of structure." (Loc. cit. p. 182.) 



Remarks on the above Evidences. — In remarking upon the physi- 

 cal evidences first, it may be stated that, excepting Becraft's Moun- 

 tain, occupying only an area of a few square miles, no sites are 

 pointed out where the " tremendous " destroying forces of the Oneida 

 period have been exerted, no line is drawn between them and those 

 which affected also the post-carboniferous period. 



In reference to Evidence No. 1 (the discordant position of the 

 Hudson-River and Medina Sandstone), the answer may be this : — 

 these rocks, being here within the range of the post-carboniferous 

 movement, as I hope to show, owe their discordancy to its agency. 



In reference to the second Evidence (the Niagara limestone lying 

 discordantly on the Hudson-River rocks in Gaspe, &c), the same 

 reply may be safely made, with this addition as concerns Gaspe : — 

 That region is 200 or 300 miles distant from the central basin of 

 New York, and is in the middle of another and wholly independent 

 palaeozoic area, which I thought was my own discovery until I found 

 it in Professor Emmons's Report ; he names it "the north-eastern 

 basin." Its base rests upon the ancient metamorphic rocks of the 

 north shore of the Gulf of St. Lawrence. From thence it sends an 

 ascending series of Silurian and other palaeozoic strata eastward across 

 Lower Canada, Gaspe, New Brunswick, Nova Scotia, and so onward 

 into the Atlantic Ocean. 



With regard to No. 3, I perhaps may be permitted to suggest 

 another cause for one portion of the statements. May not the lapse 

 of the two intermediate formations be attributed to exhaustion of 

 materials, as in the case of Oriskany Sandstone, which only spots 

 certain parts of New York ? The undulations may be claimed as 

 post-carboniferous, as in the case of Evidence No. 4. 



With regard to Evidence No. 5, stating that the Levant beds 

 (Medina Sandstone, &c.) are full of evidence of this Oneida move- 

 ment in its conglomerates and sands, I repeat that it is granted 

 throughout this discussion that there has been change of level, capa- 

 ble, in particular modes, of producing conglomerates — recollecting at 

 the same time that subterranean disturbance is not always necessary 

 to their formation. Land-floods, violent tides, or winds, a surf bat- 

 tering down a line of cliffs — any of these superficial agencies may 

 give us all the forms of rock-comminution. 



The prolonged and slightly curving outline of the Oneida Conglo- 

 merate and the Shawangunk Grit (its southward continuation) greatly 

 favours the old and well-established idea that it was the eastern bor- 

 der of a great sea gradually and curiously filled up, and occupying 

 the site of the present middle north-east America. 



The following are additional reasons (most of them derived from 

 personal observations in the field, by the Professors Rogers them- 

 selves) for believing the physical derangements of the Appalachian 

 chain ( 1 200 miles long in the United States only) took place after 

 the Carboniferous period, and not at the close of the Hudson-River 



