258 Pennsylvania before and after the Elevation  [March, 
mentioned. They are, I think, now fully accepted by all dynami- 
cal geologists. 
1. That cooling and consequent shrinkage taking place in the 
earth’s heated interior, must produce and have produced tangen- 
tial pressure in the hardened and cooled crust. 
2. That this tangential pressure overcoming the rigidity of the 
crust has produced deformation or crumpling. 
3. That this crumpling of the strata was the first and leading 
factor in the production of mountain-ranges which have been 
carved by meteoric action out of the folds this produced. 
4. That the folds out of which the Appalachian mountains 
have been carved were formed during the later part of the Palzo- 
zoic era. 
Yet further to limit the subject and bring it within the bounds 
of practicable treatment, another exclusion must be made. Mid- 
dle Pennsylvania, from Harrisburg to Pittsburgh, is occupied by an 
almost continuous succession of arches of the folded Paleozoic 
rocks. Some of these are closely pressed, others are more open, 
- some are long, ranging for many miles from north-east to south- 
west, others run only a few miles. Some involve a great breadth 
of country, others extend over only a few hundred yards. To 
take account of all these is impossible. The geography and 
geology of the State are not yet sufficiently known to supply the 
details, and the space at command is too small to discuss them if 
supplied. I therefore propose to omit all the less important ones 
and to consider only the leading mountain ranges of Appalachian 
Pennsylvania. i 
The number of these varies in different places, but not so as to 
seriously affect the results sought. Thirteen principal ridges tra- 
verse the middle of the State from north-east to south-west. All 
these may be cut by a line drawn from a point near Warrior's 
Mark in Huntingdon county, to another ten miles south-west of 
Carlisle. 
These thirteen ranges are the following: 
13. Allegheny mountain. 6. West Shade mountain. 
12. Bald Eagle “ 5. Tuscarora ? 
11. Tussey - 4. Conecocheague “ 
10. Standing Stone * 3. Bower “ 
9. Jacks x 2. Blue “ 
8. Blue Ridge. T. South s 
