GEOLOGICAL HI8TOKY OF THE COUNTY. F\ 41 



map) from the Tuscarora mountain to the North or Blue 

 mountain, a distance of 18 miles, and smoothing out the 

 rolls to their original plane.* The horizontal section meas- 

 ures about 30 miles. The loss of breadth by crumpling is, 

 therefore, 12 miles in 30 ; i. e. 40 per cent. 



Supposing this rate to hold good for the whole pala3ozoic 

 belt of middle Pennsylvania from the South mountains to 

 the Allegheny mountain, a cross distance of about 65 miles, 

 we get an original horizontal breadth of deposits equal to 

 about 110 miles; which means a movement of the South 

 mountajn line of country inland (or northwestward) for a 

 distance of 45 miles, or nearly three times the width of 

 Perry county. 



This is not the place to discuss the probable causes of 

 such a movement, but only to state the fact, which is illus- 

 trated moreover in several other ways, (1) by cracks or 

 faults in the formations ; (2) by marks on the contact faces 

 of the layers of rock, called " slickensides," grooved and 

 polished surfaces, produced by friction under great pres- 

 sure ; (3) by the disjointed condition of limestone beds bent 

 into semicircles, as at Ayl's and Baird's quarries near Bloom - 

 field ; and (4) by the distortion of fossil forms in the rocks, 

 showing how the universal movement of the mass in which 

 they are imbedded has squeezed, bent, and twisted them out of 

 shape. A large part of the fossils of Perry county are al- 

 most useless to the palaeontologist, and he is compelled to 

 piece them together and compare them with similar speci- 

 mens from other regions where the pressure has been less 

 intense or the stone less plastic. 



The great thickness of middle palaeozoic formations, and 

 their crumpled condition as above described, makes the 

 classification of the fossils in their proper places in the series 

 as difficult as it is interesting. The series of formations 

 from the Mauch Chunk red shale (No. XI) in the coves 

 down to the Utica shale (No. Ilia) in Horse valley are more 

 or less completely exposed to view. Some of these forma- 

 tions abound in fossil forms, others are exceedingly barren 



* See this method applied to one of the anthracite coal basins in Report A A., 

 1883. 



