GENERAL OBSERVATIONS. 405 



plained on pp. 104, 107. The formations are numbered — II. the 

 Calciferous ; III. Trenton; IV. Hudson River; V. Oneida; VI. 

 Clinton and Lower Helderberg ; VII. Oriskany sandstone and 

 Cauda-Galli grit. 



The mountains of Pennsylvania as well as Virginia are full of 

 such sections. In fact, they present the common features of the 

 Appalachians from Alabama to New Jersey. It is here obvious 

 that not only the Coal measures but the whole Palaeozoic has been 

 forced by some agency out of its originally horizontal condition into 

 this contorted state. The folds were mountains themselves in ex- 

 tent ; but through the extensive denudation to which they have 

 since been subjected they have been worn off and variously modified 

 in external shape, until now, as explained on page 108, it is often 

 extremely difficult to trace out the original connections. 



On the east, or towards the ocean, the folds are so pressed toge- 

 ther, and their tops so completely removed, that often only a series 

 of southeasterly dips remain (p. 107). Beyond these, the folds are 

 more separated, though still abrupt ; farther west, they diminish 

 in boldness, until they become gentle undulations ; yet there is 

 often a sudden transition to these gentler bendings along lines of 

 great faults. The following outline represents this general feature 

 of the successive folds from the southeast or ocean side across the 

 mountains to the northwest. (Rogers.) It should not be inferred 

 from this figure that the folds have the regularity here given ; the 

 preceding figures show that this is very far from the truths It 

 would also be an error to suppose that the number of folds is uni- 

 form through the length of the Appalachians. On the contrary, 

 all along their course there are folds rising and others disappearing ; 



Fig. 623. 



S.E. N.W. 



Ideal section from the S.E. to the N.W. across the Appalachians. 



they may continue on for a few miles or scores of miles, and some 

 for much greater distances, and then gradually disappear, while 

 others, more to the east or west, take their places. Thus, the Ap- 

 palachian chain is made up of a complexity of flexures following a 

 common direction. This character is well shown in fig. 624, — a 

 map prepared for this work by J. P. Lesley, who, in connection 

 with other assistants in the Geological Survey of Pennsylvania, has 

 done much towards working out the facts here presented. It gives 

 a general view of the direction and number of the folds through 

 Pennsylvania. Each line stands for the axis of a flexure. Without 



