Scientific Lectubes. 91 



the uplifting, as it is usually termed, of this belt of country. The 

 rocks are shown in abrupt foldings along the eastern and central 

 parts, while they recede to the westward in gentle undulations. It is 

 evident that no force applied directly beneath these strata could 

 have produced such a result as we see, and it becomes a question of 

 the highest interest to determine the cause which has given us this 

 structure. We cannot fail to observe, moreover, that the strata dip 

 away from the valleys and beneath the mountains ahnost invariably, 

 and that the mountains are composed of beds, not arching over their 

 tops, but dipping from each side towards the center of the mass 

 Every one of these ridges, whatever its extent, is composed of regu- 

 lar beds succeeding each other, and the whole may be examined from 

 the bottom to the top. 



I shall offer an explanation of the cause, which I suppose may 

 have produced this folding and plication of the strata ; and this cause 

 is connected with the conditions of deposition of the original sedi- 

 ments. The belt of country affected in this manner extends from 

 Nova Scotia to Georgia, and has a width of one or two hundred 

 miles. "We have seen that the sea was at all times shallow, or of 

 moderate depth. The accumulations, 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 the depression would be less in the direction of 

 the thinning margins of the deposit. By this process of subsidence, 

 as the lower surface becomes gradually curved, there must follow, as 

 a consequence of this movement, either rents and fractures upon that 

 side, or the diminished width of the surface above, caused by this 

 curving below, wall produce wrinkles and foldings of the strata. That 

 fractures may occur on the lower side, to some small extent, is proba- 

 ble ; but the folding of the strata would seem to be the natural and 

 inevitable consequence of the process of subsidence. 



The depression of the mass produces a great synclinal axis ; and 

 within the inclined sides of this greater synclinal, whether on a large 

 or a small scale, wall be produced numerous smaller syncinal and anti- 

 clinal axes. This fact is true of every synclinal axis, where the con- 

 dition of the beds is such as to admit of a careful examination. I hold, 

 therefore, that it is impossible to have any great subsidence along a 

 certain line of the earth's crust, from the accumulation of sediments. 



