ASYMMETRY OF THE NORTHERN HEMISPHERE 103 



passes over into the chain which extends across Guatemala to the Amatian 

 gulf. The Sierra Mad re has therefore a concave structure similar to the 

 southern part of the Appalachians. This changes the descriptions we 

 have formerly given of northern Central America. The whole Mexican 

 gulf and the Cambrian area of Austin (Texas) find place between the 

 two concave chains. 



New questions arise now beside the old ones, concerning the wholly 

 peculiar build of the Rocky mountains in the narrower sense (Colorado 

 Front range, etcetera) and their backward bent ranges, concerning whose 

 answer I should not now wish to venture a surmise. It is certain that 

 north of these chains in the eastern part of the mountains in Wyoming 

 movement and folding to the northeast occur, and north-northeast in 

 Montana, in 45 to 46 degrees north latitude, repeated overthrusts to the 

 east. In the same w T ay the Cordillera in Canada, as already noted, is 

 remarkable for its extraordinary overthrusts to the east. The Laurentian 

 mass is thus bordered by chains on the east, south, and west, and the 

 folding motion is everywhere directed inwardly — that is, to the west, 

 north, and east. 



Now one understands better the fact, often mentioned before, that in 

 Asia the folding is to east, south, and west ; in Europe to east, north, and 

 west. It is because the European chains form the transition from the 

 Asiatic to the American structure. 



II. 



While I again reserve for another place the thankful mention of the 

 observers who have been my teachers and the enumeration of the details, 

 especially of the structure of Asia, some of the deductions which flow 

 from the observations may be here mentioned. 



First, the very apparent contrast between Eurasia and North America. 

 The first region shows an outflow of the folds, or a motion outwardly, 

 and the second, with possible exception of the Coast ranges, an inflow 

 or motion inwardly. 



Strictly speaking, there is nothing new in this. Many of the most 

 important students of Asia, like Semenow, F. v. Richthofen, Griesbach, 

 Edm. Naumann, have each, according to his standpoint, recognized at 

 times the step-like sinking of the whole of eastern Asia on Jablonnoi, on 

 the great Kingan, and on the coastlines, at times a southward motion of 

 the whole mass, or an elevated calotte with peripheral faults ; but the con- 

 ception of a great unity of structure always appears, and often also that 

 of a more or less concentric arrangement, or a mass-motion outwardly. 



