SEGREGATION OF MATERIALS OF MOUNTAINS. 929 



Where mountain systems exist with monoclinal folds or with thrust 

 faults the segregations may be explained by shearing motion in the zone of 

 flow over an extensive adjacent area to the east of the mountain mass in 

 case the monoclinal folds have eastward-dipping axial planes, and to the 

 west of the mountain mass in case the monoclinal folds have westward- 

 dipping axial planes. (Fig. 25.) Where the folds of a mountain system are 

 symmetrical it would be necessary to suppose that the shearing motion 

 toward the mountain mass occurred on both sides of it. 



To illustrate, we may consider one of the large, simple anticlinoria, 

 such as those of the Park Ranges. We may suppose that such an anti- 

 clinorium was raised mainly in consequence of deep-seated flow toward the 

 mountain mass from either side. In this case the cleavage on either side 

 of the mountain would dip away from it. It is well known that the present 

 Park Ranges are comparatively recent uplifts along axes of old uplifts. 

 Some of the recent uplifts are partly or wholly covered by Paleozoic and 

 later strata. In the cases of these simple anticlinoria of the West the 

 cleavages of the old rocks on both sides of the anticlinal masses dip away 

 from the cores. Indeed, because of this fact, in the days when cleavage 

 was not discriminated from primary structures the cleavage was supposed 

 to be bedding, and upon the basis of this structure the mountains were 

 described as anticlinal. The present mountains we may properly describe 

 as anticlinal with reference to the Paleozoic and post-Paleozoic rocks which 

 rest upon their flanks. But since we know that mountains rise again and 

 again along the old belts, the cleavage, dipping away from the cores of 

 these mountain masses, is very suggestive that when the ancient higher 

 mountains were developed the material was segregated in consequence of 

 deep-seated flow by recrystallization toward the mountain masses, there 

 being produced at this time the divergent cleavage existing in the pre- 

 Cambrian rocks which are now at the surface, but which were well below 

 the surface when the cleavage was produced. 



The cores now exposed were covered by rocks deformed in the zone 

 of fracture and showed the deformation of joints, joint folds, faults, etc., 

 characteristic of the superficial zone. The deep-seated flowage extended 

 for an unknown distance on either side of the mountains, and thus brought 

 to the place of uplift the necessary material. The covering rocks belonging 

 to the zone of fracture on either side of the mountain range may be 

 mon xlvii — 04 59 



