504 



by the same force which has thrown the whole mountain on that side of 

 the river forward (northwestward) about two hundred yards. 



This upthrow fault, plainly exhibited by the Map, has undoubtedly de- 

 termined the point at which the drainage of the Upper Little Juniata 

 River had to pass the outcrop barrier of the vertical measures of IV 

 (Middle Silurian) now constituting the double crested mountain, called 

 Brush Mountain northwest of the Gap, and Bald Eagle Mountain north- 

 east of the Gap. 



There are similar faults connected with the issuing points of the Little 

 Juniata and of the main Juniata at their gaps through Tussey Mountain, 

 which forms the descending (S. E.) outcrop of the same measures on the 

 other side of the great anticlinal, ten miles further to the southeast. 



