36 Cincinnati Society of JSTatural History. 



heaved and eroded. And that the detached areas, even to North Caro- 

 lina, must have been part of the same estuary formation, now broken 

 up and separated through the agency of upheaval and denudation. 



Much denudation has evidently taken place, which must be added 

 to the enormous thickness which still exists to ascertain the original 

 dimensions of the deposit. All this points to a great depth of the sea, 

 or the bays, as the case may have been, in which the deposits were 

 made. 



But when we turn to the Triassic and the Jurassic of the West, we 

 observe them extending from Mexico far into British Columbia, and 

 covering hundreds of thousands of square miles. Over extended areas 

 the Triassic is more than a mile in thickness, and superimposed upon 

 it is a great thickness of the Jurassic ; and again the Jurassic is 

 found more than a mile in thickness resting upon the heav3'-bedded 

 Triassic strata. The maximum thickness, therefore, of these forma- 

 tions over great tracts of country is more than two miles, and the ques- 

 tions very naturally arise, what age do they represent ? Could the 

 deposits haA'e been rapidl}' made, and therefore represent only a brief 

 space of time, or were they extremel}'' slow and indicative of the lapse 

 of millions of 3'ears? Were the deposits made in shallow water, or in 

 the depths of mid-ocean? Is there a deposit now taking place that 

 bears any resemblance to these, and if so, what light if any does it 

 throw upon the subject? And what does palaeontology, the criterion 

 by which all rocks are to be judged, offer to enlighten us in regard to 

 the secrets of this vast accumulation of detrital material? 



All deep-sea dredgings have shown, that at great depths in the At- 

 lantic and Pacific Oceans, there is a deposit of red mud constantly 

 taking place. We think it bears some resemblance to the red sand- 

 stone of the Triassic and Jurassic periods, and in order that a com- 

 parison may the more readily be made, we quote from the most suc- 

 cessful of the many exploring and deep-sea dredging expeditions. 



Sir C. Wyville Thomson says,* speaking of the first time that the 

 dredge brought up the mud from the bottom of the Atlantic at the 

 depth of 3,600 fathoms: 



"This haul interested us greatly. It was the deepest by several 

 hundred fathoms which had yet been taken, and, at all events coinci- 

 dently with this great increase in depth, the material of the bottom was 

 totally different from what we had been in the habit of meeting with in 

 the depths of the Atlantic. For a few soundings past, the ooze had been 

 assuming a darker tint, and showed on anal3'sis a continually lessening 



'■■■ Voyage of the Challenger, vol. 1, 1878. 



