Lesley.] 



[Jan. 3, 



It will be seen from the diagram below that the geological formations 

 Nos. I, II, III and IV, resting upon each other and forming the Lower 

 Silurian system, crop out southward from under each other ; so that, No. 

 IV sandstone forms the North Mountain ; No. Ill slate, the northern half 

 of the valley ; No. II b. limestone, the southern half of the valley be- 

 tween the two railroads ; No. II a. calciferous sandrock, the foot slopes 

 of the South Mountain south of the Harrisburg and Potomac Railroad ; 

 and No. I, Potsdam slates and sandstones, the facing and top of the 

 mountain, resting on massive gneiss rocks forming the body of the 

 mountain. 



FIG. 1. 



CROSS SECTION OF CUMBERLAND VALLEY AT CARLISLE 



■§•§ 



1 



4; -5: No tl LINESTOKM BANKS 



SLATS No III. 



My object is to show that the ore deposits of the South Mountain face 

 must needs be geologically continuous. For I have in other memoirs 

 demonstrated that the ores are in fact nothing but the original rocks 

 themselves from which all or nearly all the limestone has been dissolved 

 out, leaving the clay, sand and iron behind. They are not washings of 

 ore from distant regions, dumped down at hazard in hollows of the sur- 

 face and therefore of uncertain occurrence and quantity. They are per- 

 fectly well-defined and continuous strata, occupying the position they 

 always occupied, and following the sides of the mountains, the course of 

 of the principal stream, and the strike of the harder limestone ledges, 

 along the whole course of the valley. 



They never occur in any other relationships. They are the same ores, 

 in the same rocks, arranged in the same way, the whole distance from 

 Massachusetts to Alabama. Consequently, whatever is geologically true 

 of the ore beds at Salisbury and Armenia east of the Hudson ; at Ba! Hot's. 

 Trexlertown and Moselem west of the Lehigh ; at Mont Alto and Antie- 

 tam north of the Potomac ; at Embreeville in East Tennessee ; at Shelby - 

 ville in Alabama ; is equally and in the same sense and for the same 

 reason true of the Old Bank, &c. at Boiling Spring, the Big Pond, Clever's 

 and other banks along the line of this Harrisburg and Potomac Railroad 

 in Cumberland County, Pa. 



