viii F\ REPORT OF PROGRESS. E. W. CLAYPOLE. 



sliding mass would fold itself in overturns towards the 

 bottom of the descent ; and it is also easy to see how fric- 

 tion on the rigid Azoic surface would not onl}^ limit the 

 distance at which the movement would cease, but also cause 

 the lower formations to be folded much more minutely and 

 universally than the formations higher in the series, which 

 would move with a certain freedom over them ; and this 

 may guide us to an understanding of the extraordinarily 

 close and collapsed crimples of the limestones and slates of 

 the Cumberland valley, and to the origin of the numerous 

 small folds of the roofing-slate belt of the Lehigh region. 



On the other hand, having recently constructed a model 

 of the State showing the upper surface of the Medina 

 sandstone No. IV, with all its underground arches and 

 troughs, and with these arches restored to their original 

 heights in the air, I was surprised at the clearness of the 

 testimony which it bears to the fact that a huge block of 

 the Azoic country south of Harrisburg has been moved 

 bodily north-westward at least ten miles, crushing the Palae- 

 ozoic formations into concentric circular segments, the outer 

 one having a radius of 120 miles struck from Port Deposit 

 at the mouth of the Susquehanna river ; and that to this 

 movement are due the overturn the Blue mountain rocks 

 above Harrisburg, the four-mile fault and throw along the 

 Chambersburg and Gettysburg turnpike, the McConnells- 

 burg Cove upthrow of 8000 feet, the profound synclinal of 

 the Broad Top, the great broken anticlinal at Tyrone City, 

 and no doubt the faults in Perry county, at Orbisonia, at 

 Greenwood furnace and elsewhere in middle Pennsylvania. 



Such a movement, however, involving anticlinal arches 

 five miles high, and synclinal basins correspondingly deep, 

 could not take place without greatly disturbing the original 

 thicknesses of the several formations, hard as well as soft ; 

 nor without an enormous amount of irregular shifting of 

 one formation upon another and shearing motion among 

 the groups of beds; as in fact the Anthracite survey has 

 amply demonstrated. In view of this inevitable conse- 

 quence of such a transfer of the parts of the Palaeozoic 

 system from place to place, I cannot consider it quite certain 



