———— Jaa a aaan a = 
1885.] of the Appalachian Mountains. 267 
intervals of repose is a usual mode of operation in nature. With- 
out going back to earlier days, whose events are more obscure, I 
will consider only the later geological history of our globe. And 
here are not wanting evidences of similar changes. Admitting 
that cooling and consequent internal contraction have been, by 
physical necessity, continuous, there seem to be indications that 
the subsequent corrugation of the crust has been to some extent 
spasmodic. Beyond doubt the formation of arches and troughs 
by compression of the strata has occurred in almost every era. 
Perhaps when we know the whole earth we may find no time of 
perfect repose. But since the Palzozoic era ended there has been 
at least one period during which the process again rose into great 
prominence, eclipsing perhaps that which it exhibited in Palzo- 
zoic days. Anticlinal arches can be found of almost every date 
in Secondary time. But after the beginning of the Tertiary age, 
and through a great part of its duration, their development be- 
came wonderful. Almost all the great mountain ranges date from 
this era. Strip from the earth the mountains of Tertiary date 
and it would lose nearly all its grandest features, and would be 
reduced to a comparatively monotonous plain. The Rocky 
mountains and the Andes in the western world, and in the east 
the Alps, the Apennines, the Pyrenees, the Carpathians and the 
Himalayas, with other minor chains, all date back to about Mid- 
tertiary days. And the elevation of so many lofty anticlinal 
folds, in comparatively a short time, threw into the shade all 
events of the kind that had occurred since the great Appalachian 
revolution. It is not yet possible to estimate, still less to mea- 
sure, the folds of these ranges, but it impossible to doubt that 
they would yield results scarcely less, and perhaps greater, than 
those which I have given for Pennsylvania. 
- What then must be our conclusion? Must we incline to the 
belief that our earth has much diminished in size.since the middle 
of Paleozoic time? Must we admit that this diminution amounts 
to many miles? That the radius is thirteen miles shorter than it 
then was, and the circumference less by six times that amount? 
Apparently there is no escape. 
One word more. Is not the admission amet ? Is not the 
denial unreasonable? If the earth is a cooling and contracting 
globe the result must surely be evident in the long ages that have 
elapsed since the Appalachian earth-folds arose. If the corru- 
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