r» PALiEONTOLOGY OP NEW-YORK. 



these accumulations. On the contrary, the evidences from ripplemarks, 

 marine plants, and other conditions, prove that the sea in which these 

 deposits have been successively made was at all times shallow, or of 

 moderate depth. The accumulation, therefore, could only have been 

 made by a gradual or periodical subsidence of the ocean bed ; and we 

 may then inquire, what would be the result of such subsidence upon 

 the accumulated stratified sediments spread over the sea bottom ? 



The line of greatest depression would be along the line of greatest 

 accumulation ; and in the direction of the thinning margins of the 

 deposit, the depression would be less. By this process of subsidence, as 

 the lower side becomes gradually curved, there must follow, as a con- 

 sequence, rents and fractures upon that side ; or the diminished width 

 of surface above, caused by this curving below, will produce wrinkles 

 and foldings of the strata. That there may be rents or fractures of the 

 strata beneath is very probable, and into these may rush the fluid or 

 semifluid matter from below, producing trap-dykes ; but the folding of 

 strata seems to me a very natural and inevitable consequence of the 

 process of subsidence. 



The sinking down of the mass produces a great synclinal axis ; and 

 within this axis, whether on a large or snjall scale, will be produced 

 numerous smaller synclinal and anticlinal axes. And the same is true of 

 every synclinal axis, where the condition of the beds is such as to 

 admit of a careful examination*. I hold, therefore, that it is impossible 

 to have any subsidence along a certain line of the earth's crust, from 

 the accumulation of sediments, without producing the phenomena which 

 are observed in the Appalachian and other mountain rangesf . 



That this subsidence was periodical, we have the best possible evi- 

 dence in the unconformability of the Lower Helderberg group upon the 

 Hudson-river group ; showing that previous to the deposition of these 



* I am indebted to Sir William L' can fur this latter suggestion, as tlic result of his very accurate and 

 exteniire observations on the relations of anticlinal and synclinal axes. 



t To have an idea of this folding, it is only necessary to take a package of flat sheets of paper, and 

 hold the edges flrmly in the same position and relation they had when in a horizontal position, de- 

 pcvMing the centre, and as the lower sheets assume the curved direction the upper ones will curve 



