398 PALEOZOIC TIME. 



much greater distances, and then gradually disappear, while others, 

 more to the east or west, take their places. Thus, in the Appalachian 

 chain, there is a complexity of flexures following a common direction. 

 This character is well shown in Fig. 703, — 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 toward 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 claiming absolute accuracy, it gives a 

 correct general idea of the number and positions of the folds in this 

 part of the Appalachian region. 



The following are some of the most important facts established with 

 regard to these Appalachian flexures : — 



1. They occupy the whole Appalachian and Eastern-border regions 

 of the continent, nearly or quite to the Atlantic Ocean. 



2. They are parallel with the general course of the mountains, and 

 nearly with the Atlantic coast. 



3. They are most crowded and most abrupt over the part of the 

 regions which is toward the ocean, — that is, the southeast side (Fig. 

 702. 



4. The steepest slope of a fold is that which faces the northwest, 

 •or away from the ocean (Figs. 701, 702). 



5. They are in numerous ranges ; but, while some are of very great 

 length, there is in general a commingling of shorter flexures ; and 

 often they are in groups of overlapping lines (Figs. 12 to 17), as ex- 

 plained, with reference to the arrangement of the parts of mountains, 

 on pages 19 and 20. 



6. Although many of the folds were like mountains in dimensions, 

 they have been so worn and removed by denuding waters — either 

 those of the ocean, or rivers, or both — that the higher parts of the 

 folds do not generally form the summits of existing elevations. The 

 fissures of the broken mountains would have been deepest and most 

 numerous in the axes of the folds ; and hence denudation has been 

 most destructive along the more elevated portions. 



2. Faults. — Besides the remarkable plication of the earth's crust 

 in this Appalachian revolution, numberless fractures and faults or dis- 

 locations occurred over the whole region, as was natural under the 

 contortions and uplifts in progress. Some of the faultings were of 

 great extent, lifting the rocks on one side of the line of fracture 

 5,000 or 10,000 feet above the level on the other side. The faults 

 mentioned on p. 214 are of this character ; and part of the series there 

 alluded to was probably made at this time. There is one of these 

 great faults west of the eastern range of the Cumberland Mountains, 



