No. 161.] 
205 
ges for the examination of the transition and primitive classes, as 
in our highly favored country. Our series of rock masses are few, 
their range is uninterrupted, with partial exceptions, from the 
north to the south, and from the east to the west, almost through- 
out the whole Union. This is owing to our having but one gene- 
ral direction for our range of mountains, and these mountains of 
limited elevation, whose uplifting being the chief cause of the de- 
rangement of the original position of our rocks, its disturbing in- 
fluence to the west has not extended much beyond the region of 
anthracite coal. 
2dly. To the absence of another disturbing cause, that of local 
volcanic action. The fact is truly remarkable, in an extent of 
country so great, for within the limits of the States there are none 
known, excepting those of an age coeval with the range of the old - 
red sandstone of Mr. Maclure, east of the mountains, and seeming- 
ly confined to that range. 
3dly. To the uplifting bodily of the whole west, without de- 
rangement productive of difficulty to the examiner, followed by sub 
» sequent denudation in the direction of Lake Ontario, which so un- 
covered the rocks of the third and fourth districts, as to present a 
series of broad steps or terraces, over which, in going from south 
to north, in descending from one to another, you ascend in their 
chronological order. 
Lastly. To the absence of an almost entire cla'ss of rock, com- 
prising all that part of the secondary, between the coal and the 
cretaceous group, or chalks of Europe, which, forming as it does, 
by far the larger part of the surface of that continent, and from its 
computed thickness, in England, of two thirds of a mile, will give 
some idea of the advantage of their absence, for the study of older 
rocks. The presence of the secondary class, of the same compa- 
rative extent as in Europe, with the same thickness, on the autho- 
rity of the Reverend Mr. Buckland, as in England, would, if su- 
perimposed upon our rocks, so depress them as probably to be be- 
yond the reach of our observation. The elevation of our rocks, 
being owing to geological dynamics, and their retention at their 
present elevation, to the equilibrium of opposing forces. 
This absence, in so large a portion of the United States, of those 
more recent rocks, which elsewhere form so large a portion of the 
earth's surface, conclusively shows, that as all that part was up- 
