262 Pennsylvania before and after the Elevation [March, 
been so crushed and compressed that its present breadth along 
the line of section is only sixty-five miles. Of this shortening 
the greater part has been suffered by the Cumberland valley, 
where ninety-five miles of country have been compressed into 
sixteen miles. 
The diagram shows the distribution of the compression among 
the different counties. Approximately it may be represented by 
the following figures : 
ORIGINAL AND PRESENT EXTENT OF THE COUNTIES ALONG THE LINE OF 
SECTION 
Original extent. Present extent. 
Blair..... a i i 
a a T E E ere se Pee ae 26 « 24 oa 
MG 0. care Us pebIeS. os He. Gs 6 « 
Juniata ; ee ¢. s 8 66 
Perry oe 12 ét 9 
58 49 
Cumberland , oas e 16 4 
153 “ec 65 (Zi 
These facts may be thus expressed. During the compression 
and corrugation of the crust to which the mountains of Pennsyl- 
vania owe their origin, the south-east line of Huntingdon county 
was moved forward two miles, that of Mifflin four miles, that of 
Juniata six miles, that of Perry nine miles and that of Cumberland 
eighty-eight miles. Consequently the whole of Mifflin county 
was shoved, at the least, two miles to the north-west, the whole of 
Juniata county four miles, the whole of Perry county six miles 
and the whole of Cumberland county nine miles over the under- 
lying deeper strata. The possibility, still less the reality, of 
mass-motion of this kind and to this extent, has not, it seems to 
me, been generally recognized by geologists. 
The movement of course diminished toward the north-west in 
consequence of the increasing resistance offered by the increasing 
load, and came at length to nothing beyond the limits of Penn- 
sylvania. Ohio was the great buffer-plate against which this tre- 
mendous earth-force spent itself. The south-eastern portion of 
_ the district—the Cumberland valley—and even probably some 
Saat considerable area beyond it to the south-east felt its first and 
~ mightiest pressure. There the strata were crumpled, bent, crushed 
- and thereby thickened until it became easier to shove them bodily 
_ forward than to bend them again. They were consequently added 
