232 C. E. LOXGWELL KOBER's THEORY OF OROGEXY 



have pressed against or toward each other, squeezing the relatiYely plastic 

 orogenetic zones and thus localizing folded mountains. 



Theory axd AVork of Suess 



In studying the genetic relationships of mountains it is especially 

 important that we recognize the largest units of structure. Exactly 

 what constitutes a complete orogenetic zone and what does it look like 

 in cross-section? Since the time of Suess we have been impressed with 

 the asymmetry of folded mountains. It is a common conception that 

 they are one-sided, the expression of intense rotational forces. Thus 

 we speak of the Appalachians as overturned to the west, the Alps to the 

 northwest, the Himalayas to the south, the Andes and northern Eockies 

 to the east. This asymmetric cross-section is nowhere more pronounced 

 than in the famous ''decken*^ structure of the Alps, revealed in the 

 ^'mountains without roots,'^ which are isolated masses of older rocks 

 standing on a base of more recent formations. It is clear that these 

 anomalous masses are remnants of great overthrust sheets or recumbent 

 folds,- which were pushed northward many miles from their original 

 positions. Deep erosion has exposed a series of these sheets, or even 

 local repetitions of a series, with rocks ranging in age from pre- Cambrian 

 to Tertiary lying in various combinations of superposition. The com- 

 plex mass has been rolled forward over the foreland, wliich shows 

 depression under the load. 



CoMPARisox OF Views of Suess axd Kober ox the Mediterraxeax 



MouxTAix Syste:m 



Suess pointed out that several mountain systems in the Mediterranean 

 region may be considered as parts of a much larger unit. The trend- 

 lines of the Alps are continued through the Carpathian arc into the 

 Balkans, forming a sinuous but practically unbroken system, with over- 

 turning in the same sense throughout. Suess also saw a westward con- 

 tinuation of the Alps through the Apennines, the Atlas, and the Betic 

 Cordillera of southern Spain. Thus he "pictured the Alpine system as 

 a great spiral, Avith its center near (Tenoa." But Kober contends that 

 the Pyrenees and not the Apennines are the proper westward continua- 



- Kober evidently favors the older conception of Swiss geologists, that the great 

 "decken"' are attenuated recumbent folds rather than overthrust plates. He recognizes 

 a difference in structure, however, between certain "decken."" as the Helvetian, 

 apparently developed at a shallow depth, and others, as the Pennine, evidently formed 

 under great load. 



" He recognized the reversal in direction of overturning in passing from the Maritime 

 Alps to the Apennines. 



