IN THE DEGRADATION OF THE LITHOSPHERE. 395 



by the conventional lines of anticline and syncline structures,'*^ a 

 geosyncline, for example, or anticline would develop into a series 

 of fractures in the outer portion of the lithosphere if the pressure 

 which made the original fold were to continue or were to be applied 

 without a heavy series of overlying beds. The zone of flowage 

 would become a zone of fracture by release of pressure from above 

 without necessarily there being a release of other strains in the 

 mass of the rock. To make a practical application, the Appalachian 

 folds and the fan-shaped folds of Heim, in the Alps, are often 

 represented in diagrams as having developed as surface folds of 

 the lithosphere, that is, it is practically stated that we might con- 

 ceive a portion of the outer lithosphere structure to be practically 

 destitute of faults from the fact that the rock structures under 

 pressure assume a fold-flowage structure. Thus, in Fig. 285, in 

 Pirsson & Schuchert, p. 362, the evolution of the Appalachian moun- 

 tains is represented as having occurred as a series of zones of 

 surface folding followed by erosion of the folded zone producing 

 the usual peneplane. This I conceive to be at least an unlikely 

 series of developments in spite of the weight of the authority back 

 of the theory. 



If the pressures which developed the Appalachians took place 

 in a mass so that folding and flowage took place, we would almost 

 of necessity have to suppose a heavy super-incumbent mass of rock, 

 so that instead of fracturing taking place the rocks under the intense 

 pressure would move by lines of flow ; on the other hand if the 

 above pressure were applied to a mass of rock without this heavy 

 overlying weight, then fracturing would almost certainly have to 

 follow. So, if in such a mass as the Appalachians where the force 

 of the uplift continued through a long period of geologic time, with 

 processes of surface erosion proceeding, it is an allowable supposi- 

 tion to believe that the zone of flow would pass upward into a zone 

 of fracture and expose the outer portion of the lithosphere to a 

 much more rapid means of degradation than would follow from the 

 usual processes of erosion and degradation on an unfractured mass. 

 So that the zone of flowage in this case, and it would apply to other 



45 See. for example. Figs. 285-291, Pirsson and Schuchert, "Textbook of 

 Geology." Also Dana and others. 



