11 J. D. DANA — A.REAS OF CONTINENTAL PROGRESS. 



pan region referred to was nearly 200 miles in length from east to west, and 

 that of the shallow Bea-flata of the Water-lime over three times this length. 



The western passage way, or that over Michigan and Northern Ohio, was 

 again deep and widely open through most of the Corniferoua period. After- 

 ward there was again a narrowing and a shallowing. It is' easy, with the 

 geological reports of the State of New York and those of the other States 

 along the Eastern Interior region, to follow out the various changes that 

 came over the area and its western open way, and also the coming on of the 

 area of alternating emergences and submergences characterizing the coal 

 period. I have been over the records, but have to confine myself here to a 

 few prominent point.-. 



The conditions of such a bay during the Upper Silurian, Devonian, and 

 ( arboniferous eras would have influenced tide-, currents, temperature and 

 parity of waters, sediments, life, and everything that could have affected 

 rock-making and biological distribution. The conditions were varied, also,_ 

 by oscillations in the water-level, and here and there by the throwing up of 

 long beach-made or sand-flat barriers. In either way, great shallow confined 

 seas, like Pamlico Sound and others of the Atlantic border, but perhaps 

 larger, mighl at times have existed, especially as the waters became more 

 shallow ; and such seas would have been likely to vary from purely marine 

 to intensely briny, on one side, and to brackish and fresh on the other. 



These few particulars are enough to make it manifest that the consequences 

 of the geographical conditions in the Eastern Interior sea must have been of 

 most comprehensive range. 



As regards life, the head of the Eastern Interior region, comprising the 

 area of New York and Pennsylvania, would have been the least favorable 

 of the whole Interior Continental sea for pure-water species. Whenever 

 depth and purity of water favored, such sp vies would have gone in ami 

 flourished and made limestone, as they did during much of the Niagara and 

 < ' irniferous periods. But, in general, pure-water species would have been, 

 and were, absent. The species outside would have migrated in or not accord- 

 in.: to their habits, and readily, for where there are tides and currents migra- 

 tion of marine species is rapid work. lint under BUch circumstances the 

 stratigraphical succession could nit correspond to tie- true biological sue 

 sion of species. It would be only local-condition succession. Prof Henry 



9 William- established this conclusion fully by the facts from the Devonian 



of New York which he presented to the A.merican Association in bis very 

 valuable paper of 188 i, and Prof. < '. L. Herrick has recently drawn atten- 

 tion to similar facts and presented explanations of similar import/] They 



►H.8. Wl i •- ,,( iii.' Inter, \ 



IN in nan, ibid. 1884, i 



■ ' • l- Herrick, iIob 'in... Hull.- i i I r, Vol. IV, p. 97, In a 



niiriu.'l from Voli, II nil.) III Mr Hen ries ..i " 



logical :i|.li..n-.in-,' on pag •• ili.' prlnci] ted. 



