240 



C. R. LONG WELL KOBER's THEORY OF OROGENY 



farther on the foreland and cover the area in front with their decken wall, 

 or thrust it forward, squeeze it, overturn it. Phases of quiet follow intensified 

 mountain-making. This is all plainly expressed in the sediments. The brec- 

 cias always originate during the phase of unrest ; they define the manner of 

 mountain-making as to time and place, and are therefore valuable guide 

 horizons in unraveling the genesis of a decken mountain system. The con- 

 ditions of sedimentation become increasingly complicated with the evolution 

 of decken. Out of the rubbish of the decken, strata may form on the sea- 

 floor, which in turn are made into decken. 



"The decken movement is from the inner parts of the geosyncline outward, 

 and it advances continually against the rigid plates of the foreland. This 

 also may be included more or less in the powerful movement and drawn into 

 the whirlpool of the orogenic field of force. The more the geosyncline is 

 compressed, the more will it rise as mountains and become terra firma. 

 There follows the phase of arching up the decken ranges into lofty mountain, 

 chains. Steinmann has designated this phase as positive mountain-making. 

 According to Heim, this phase is followed by a further one, which is char- 

 acterized by the sinking of the mountain chain, immersed like an iceberg in. 



ViGVRK 8. — Schaita des Grahen-Horsitypus 

 Kober's figure 1, page 51. 



the sea, as a consequence of its enormous size and weight. This is a sort of 

 closing phase in the making of a young decken mountain system. Perhaps 

 this may be designated as the negative phase. The positive phase is char- 

 acterized by the division of the mountain system into blocks ( Schollen ) . The 

 mountain chains rising out of the sea remain for a long time near sealevel, 

 and undergo there widespread planation, as is seen in the East Alps (pre- 

 Miocene, pre-glacial surfaces). The Alps at that time had not the character 

 of a high mountain system. They were rather a hill country or mountains of 

 moderate height. Only positive mountain-making forced the Alps to great 

 heights. It is said that these movements are epeirogenic. As a matter of fact, 

 they are expressed chiefly in fractures and flexures, in arching of the old land 

 surface. But these epeirogenic movements, as was stated previously, are 

 disguised orogenic movements, involving fractures which may later become 

 overthrusts. In any case they are not movements of an entirely different 

 sort, but merely continuations, through a .short time interval, of the orogenic 

 or decken movements." 



