LETTER OF TRANSMITTAL. F 2 . IX 



that the remarkable disappearance of outcrops (Marcellus, 

 Oriskany, Little Helderberg and Upper Onondaga) along 

 the line of the overturn — that is along the Blue mountain 

 for some miles west of the Susquehanna river in Perry 

 county and for some miles east of the river in Dauphin 

 and Lebanon counties — can be wholly explained by an 

 original lack of the sediments in a shallow or dried up sea. 

 It is very remarkable that this failure of the formations 

 should happen just along the line of maximum thrust and 

 slide, — just where the whole mass was turned over beyond 

 the vertical upon its face, — therefore, just where the greatest 

 amount of shearing motion must have occurred, — in fact, 

 just where we should expect an upthrow fault with all its 

 consequences. 



Prof. Claypole has presented the arguments for shallow 

 water on pages 37 and 393 ; and they have force ; but there 

 are dark places in the line of argument of this question 

 pursued by geologists in other parts of the world ; and the 

 evidence from pebbles must be considered of little weight 

 since the researches of M. Delesse in the waters of the bay 

 of Biscay, and the remarkable discoveries of large pebbles 

 in considerable numbers in very deep water off the Atlantic 

 seaboard made by the dredging parties of the U. S. Coast 

 Survey and published recently by Prof. Verrill. Even the 

 coralline beds of the Lower Helderberg, mentioned on 

 pages 160, 182, 338, are not conclusive evidence of shallow 

 water, unless it be proved that the original reef-is in place. 

 Detritus of coral reefs is carried far out into deep water ; 

 and the multitudes of disjointed encrinite stems found in 

 the Lower Helderberg and Hamilton formations (pp. 62, 206, 

 260, 343) may have been distributed over a deep ocean bed. 



Xo geodetic instrumental work has been done in Perry 

 county. Consequently the limits of the outcrops of the 

 formations are drawn only provisionally upon the town- 

 ship maps (which are not very reliable) and must be cor- 

 rected by the local knowledge of the citizens of the county. 

 They will serve very well for a description of the geology 

 of the county, but must not be relied upon for local explo- 

 ration. They will be very useful to guide explorers in a 



