234 ROLLIN T. CHAMBERLIN 



The total length of the Oriskany stratum as reconstructed in the 

 cross-section from the west end of the folded region to Mount Union 

 (Figs. I and 2) was found to measure 2,602 millimeters. The 

 straight-line distance between these points measured on the railroad- 

 level is 2,288 millimeters. The length of the top line of the restored 

 section (the top of the Pottsville) was also measured as a check. It 

 was found to be 2,618 millimeters. If 2,602 millimeters, the length 

 of the Oriskany along the dip, represents the original length of that 

 stratum before the folding took place, and 2,288 millimeters represents 

 the present horizontal length of the section under consideration, there 

 must have been a shortening of this formation to the extent of 314 

 millimeters, or 12 per cent, of the original length. On the scale used, 

 seventy-six millimeters in the cross-section represents one mile in 

 nature. Converting the figures obtained from a measurement of 

 the plotted section into miles, the length of the Oriskany (2,602 

 millimeters) becomes 34.2 miles and the horizontal distance, 2,288 

 millimeters, is equivalent to 30.1 miles. Neglecting other factors, 

 the shortening amounts, therefore, to 4 . i miles. 



In the second section the length of the Oriskany from the beginning 

 at Lewistown to the crest-point of the anticline above mentioned 

 between Baileysburg and Iroquois Station was found to measure 

 1,789 millimeters. At this point the shift was made to the base of the 

 Catskill. The lower limit of this formation, followed to the point 

 where it rises above the railroad-level about half a mile southeast of 

 Marysville, gave a dip distance of 1,070 millimeters. The sum of 

 these two dip measurements gives 2,859 millimeters as the length of 

 these strata between Lewistown and the contact of the Catskill with ' 

 the Chemung close to the Susquehanna bridge five miles above 

 Harrisburg. On the same scale the present horizontal distance 

 between these points is 2,399 millimeters. This indicates a crustal 

 shortening due to the flexing of the beds, which amounts to 460 milli- 

 meters, or 16. 1 per cent, of the original length. Translated into miles 

 these figures are respectively 37.6 and 31.5 miles, signifying a 

 shortening of 6 . i miles. The total shortening, therefore, from the 

 beginning of the section west of Tyrone to the point between Marys- 

 ville and the Susquehanna bridge amounts, on the basis of the 

 assumptions made, to 10. 2 miles, 71.8 miles having been compressed 

 to 61.6 miles. 



