98 J. D. Dana on the origin of some of the 



bearing evidence of man's agency in their accumulation ; or (4) if 

 tlie sinking is one now in progress, it should be apparent in the fact 

 that the waters have deepened in historic times over submerged rocks, 

 or in harbors. No proofs of such a sinking have been observed, and 

 no one among those who have had the most to do with the coasts 

 has suspected that any is now in progress. 



The fact that the plain extends quite to the western hills, without 

 any higher margin or range of beaches along these hills, is the strong- 

 est argument for the supposed sinking, that is, a sinking greatest to 

 the southward. 



(4.) Slope resulting from an increase in the amount of ele- 

 vation TO THE NORTH. — The great differences in the height of the 

 drift formation in the Quinnipiac and Mill River valleys have shown 

 that the slope in the surface of the latter is not due solely, or mainly, 

 to an elevation of the land that was greatest to the north. The facts 

 in Mill River valley would require, if this were the cause, an average 

 increase in the rise northward of 1 1 feet a mile between Whitney- 

 ville and Mount Carmel; and those of the Quinnipiac, even taking the 

 normal height of the terrace of North Haven at 50 feet, of but a foot a 

 mile. Still it is possible that some part of the slope of the land is 

 attributable to this cause, and even probable in view of the fact that 

 the rise affected cotemporaneously all New England, and resulted in 

 raising its northern portions, especially the northwestern, the most — 

 the increase from New Haven, by Lake Champlain, to Montreal 

 averaging 1^ feet a mile. Judging from the increasing height of the 

 terraces to the northward along the rivers of Connecticut and Massa- 

 chusetts, it does not appear probable that the increase per mile in 

 southern New England exceeded one foot a mile. Adopting this 

 rate for the New Haven region, the average slope of the part of the 

 plain along Mill River valley, south of Mt Carmel, would be reduced 

 to 10 feet a mile, and that of the part of the Quinnipiac south of North 

 Haven, nearly to a level surface. 



(5.) Conclusions WITH regard to the Elevation. — The follow- 

 ing are the conclusions to which we are led with regard to the amount 

 and character of the elevation. 



1. That it was rapid if not abrupt, at least for the first 25 feet. (Pro- 

 gress for a century or two would be geologically rapid.) 



2. That it was 45 to 50 feet, probably 50, in amount. 



3. That the formation of the northern part of the plain, beyond 50 

 feet in elevation is due mainly to the floods of fresh water filling the 

 valleys and spreading widely over the plains during the melting of 

 the great glacier of central New England. 



