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PALAEONTOLOGY OF 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 small 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 Logan for this latter suggestion, as the result of his very accurate and 
extensive observations on the relations of anticlinal and synclinal axes. 
| To have an idea of this folding, it is only necessary to take a package of flat sheets of paper, and 
hold the edges firmly in the same position and relation they had when in a horizontal position, de¬ 
pressing the centre, and as the lower sheets assume the curved direction the upper ones will curve 
