INDUSTRIAL PROGRESS DURING THE YEAR 1872. xxxv 



the latter, together with the Clinton, Niagara, and Salina 

 groups, all thin out to the eastward, in which direction they 

 were limited by the barrier of dry land composed of the rocks 

 of the Cincinnati group. The Clinton, Niagara, and Salina 

 formation, as Hunt has shown from their chemical composi- 

 tion, were all deposited in an inland basin cut off from the 

 open sea, and consist of magnesian limestones, with salt and 

 gypsum beds. This order of things was terminated by a 

 great movement of depression, as a result of which the free 

 ocean waters flowed over the former eastern barrier, so that 

 the limestones of the Lower Helderberg period are resting 

 unconformably on the different members of the Cincinnati 

 group along the valleys of the Hudson and the St. Lawrence, 

 and even among the ancient crystalline rocks of the Appa- 

 lachian region in New England and the British provinces. 

 This depression was the beginning of a new order of things, 

 whose continuation is seen in the Corniferous limestone and 

 the Hamilton shales, the rocks of the Erie division of the New 

 York system the so-called Devonian, to which Dawson has 

 proposed to give the more appropriate name of Erian. The 

 flora of this period, brought to light by Hall in New York 

 and Newberry in Ohio, has been carefully studied by Dawson, 

 and gives us a most important chapter in pala3ophytology. 



The great geological revolution which marks the break 

 between the rocks of the second and third faunas in Ohio 

 and in New York is, as Hunt has shown, but a repetition of 

 a similar process which took place at a still earlier period, 

 and gave rise to the break between the strata of the first 

 and second faunas along the eastern part of the great palaeo- 

 zoic basin. The Potsdam, and Calciferous, and Chazy forma- 

 tions of northern New York and Canada are the thinned- 

 out representatives of the great series of strata designated 

 the Taconic by Emmons, the Quebec group by Logan, and 

 the Primal and Auroral by Rogers, and include the first pa- 

 laeozoic fauna. The Calciferous sandrock was evidently form- 

 ed under conditions similar to the Niagara and Salina forma- 

 tions, and is, like these, a magnesian limestone with gypsums 

 and brine-springs. The succeeding Chazy limestone is a local 

 formation marking a passage to the new order of things, 

 when, by a great change of level, the open ocean of the Tren- 

 ton period invaded the region, and, extending far beyond the 



