248 



conform to the existing features, would be far greater than would 

 be needed to bring the imaginary subsidence-area to a like agree- 

 ment. In the latter conditions, the denuding force would be 

 called on to remove only a certain amount of material below the 

 horizontal surface over the northern portion of the tract ; in the 

 former, it would have first to cut- down the greatly elevated out- 

 crops at the north to bring them on a level with the southern 

 deposits, and after this to do an additional amount of excavation 

 equal to that of the other surface. 



Admitting the validity of these arguments drawn from obvious 

 mechanical and stratigraphical relations, we must conclude that 

 the remarkable preservation of the paleozoic strata in the region 

 referred to has been due to the subsidence which successively re- 

 moved them in great part from the destructive effect of shore- 

 action, sealing them down under an accumulation of overlying 

 deposits. This preservation, therefore, is entirely consistent with 

 the view of Darwin and other geologists, of the extensive destruc- 

 tion of deposits with their fossils, when, through an uprising move- 

 ment, they are brought, stratum by stratum, within reach of the 

 wasting and dispersing forces of the shore. It certainly affords 

 no argument in contravention of that doctrine. 



In maintaining that these paleozoic rocks were accumulated 

 during a period characterized, on the whole, by a great aggregate 

 subsidence of the ocean-floor. Prof. Rogers was far from suppos- 

 ing this movement to have been regular, or without pauses and 

 reversals. He believed that the materials of the successive great 

 formations bear intrinsic evidence of repeated long pauses, and 

 that the transitional deposits are marked by the proofs of occar 

 sional, and perhaps frequent, upward oscillation. During these 

 subordinate pauses and upward movements, themselves occupying 

 periods of great absolute length, however small in comparison 

 with the whole, we may well conceive that many extensive sheets 

 of the previous deposits were disintegrated and dispersed, and we 

 may fairly infer that the existing series of strata, with all their 

 seeming fulness, are but an imperfect and fragmentary record of 

 the life-history with which they are impressed. 



Prof. Agassiz maintained that there was not subsidence during 

 the deposition of the New York strata, and that the facts do not 



