252 



TRANSACTIONS OF THE 



The section of the mountain was drawn from observa- 

 tions made along the railroad, but projected to a vertical 

 plane passing through the line of dip. The base line 

 represents the level of the Atlantic ocean. The road is 

 shown by a red line. The section also shows the beds 

 of Blair's Gap run and the Conemaugh ; the form of the 

 ground in the vicinity of the railroad, with the ravines 

 and streams which cross it ; and the general outline of 

 the mountain. The horizontal scale is 3000 feet to an 

 inch; and the vertical scale 500 feet to an inch. Allow- 

 ance must of course be made for the distortion caused by 

 so great a difference between the scales. 



The section extends between the points marked A 

 and B on the map. Along this whole distance the line 

 of dip was taken at a great many points, and found to be 

 singularly regular. Its direction is W. N(. W,, w^hich 

 makes the line of bearing very nearly correspond with 

 the average course of the mountain crest. The dip does 

 not vary materially from inclined plane No. 3 to inclined 

 plane No. 6 ; for this distance it is 3| degrees. From 

 inclined plane No. 6, it increases gradually as we pass 

 eastward ; and at HoUidaysburg, which is the most eastern 

 point shown on the section, it is 23 degrees. 



The drawings show strikingly the manner in which 

 the sides of the mountain have been cut down by the ac- 

 tion of water, which has made deep narrow valleys, some- 

 times destroying large quantities of coal. These denu- 

 dations have been productive of one good effect however ; 

 for they have exposed some of the lower strata in the 

 series, which otherwise could not have been worked 

 except at great expense. 



A box of specimens, with references to the section for 

 the strata in which they were found, accompanies these 

 papers. Blare minerals will not be looked for from this 

 quarter, and the specimens are valuable only as illustra- 

 tions of an interesting formation. 



4 



