Page:Popular Science Monthly Volume 7.djvu/410
THE POPULAR SCIENCE MONTHLY.
relation to the surface of the sea, so that upheaval or throw is only relative to this general standard of comparison. But during the geological ages represented in the folding and carving of the Uinta Mountains, it is possible the level of the sea itself has been changed by the shrinking of the earth, and a part, at least, of the apparent upheaval above mentioned may be accounted for by a depression of the formations in synclinal folds, and the letting down of broad areas of the earth's surface by lateral contraction exhibited, in corrugation.
It has already been said that the cutting off of the fold has left the upturned edges of the formations exposed to view. Some of these beds are quite hard, others are composed of very soft material; so that there are alternating beds of harder and softer rocks running in an easterly and westerly direction, both on the north and south side of the range. The soft rocks, yielding much more readily to atmospheric degradation, have been washed out in irregular valleys, between intervening ridges of harder rock, so that we have a series of nearly parallel valleys, and also a series of intervening parallel ridges, and both valleys and ridges are approximately parallel to the range. But, as the great fold of the Uinta Mountains is greatly complicated