382 



C. SKOTTSBERG 



the deep trench following the trend of the Andes, is a consequence of the gigan- 

 tic mountain-building processes, the submarine ridges west of the trench can- 

 not help to get implicated. This idea is by no means new, it has been expressed 

 by many: "the width of South America may well be a good deal less now than 

 before the Andes were uplifted", as GoOD says [log. 349), but some of these 

 writers did not try to penetrate the complicated geographical-geological history 

 of this region of great tectonic disturbance. This is true of myself, when I tried 

 to describe what I imagined having occurred [22y. 43), but it does not apply to 

 Irmsciier (/</?) who took pains to inform himself of the history of the Andes 

 as told by geologists. That they arose in a geosyncline is proved by the Jurassic 

 and Cretaceous beds now elevated thousands of meters and covering the older 

 eruptives. To the east of the depression land had existed since the Permian, to 

 the west was a Pacific land mass of hypothetical width; one opinion regarded 

 the Coast Range as belonging to this land. IRMSCIIER, who took Wegener's 

 side, did not ask I'or any large-scale subsidence correlated with the uplift of the 

 Andes, because the resistance of the sialic crust to the westward drift of South 

 America was sufficient to account for uplift and folding. Consequently, he was 

 unwilling to accept Penck's intrusion theor\-; if, in the future, it should appear 

 essential to accept a land mass, it could be nothing more than a narrow strip 

 w'hich, perhaps, had been connected w'ith California (p. 45). 



Penck stellte die Ausbildung der ozeanischen Tiefen am Rande des siidanierika- 

 nischen Kontinentes, also das Versinken angrenzender Teile des Fazifiks, der aufwarts 

 bewegten andinen SchoUe gegeniiber und schhesst, dass die niichstliegende Erkliirung 

 fiir die Volumenanderungen unter der festen Kruste in dort stattiindenden Massenver- 

 schiebungen zu suchen ist. Wenn Massen aus der pazifischen Region in die andine 

 iibertreten, so muss in ersterer die Kruste nachsinken (p. 51). 



The cause of the uplift and folding was, according to Penck, a result of 

 the intrusion of the andesitic magma, which lifted the mountains but, IRMSCHER 

 remarks, this could not be the only source of the tangential pressure: 



Die mechanischen Ursachen des Faltenvorganges sind zweifellos anderer Natur, und 

 die Magmaintrusion ist genau so eine Wirkung derselben wie die Faltung. Denn es steht 

 test, dass die Gebirgsbildung mit dem Empordringen des Magmas synchron ist und die 

 Intrusion somit gleichzeitig mit der angenommenen ahmahlichen Lostrennung Siidamerikas 

 von Afrika. 



Where does the Chaigneau-Merriam bank come in.' WEGENER left it unexplained, 

 according to Du ToiT it was an "advance fold". 



Berry and Singewald [2^], in their review of the tectonic history of South 

 America, describe the development in the following terms. 



Some students regard the Cordillera de la Costa in Chile as remnants of an an- 

 cient massif, the bulk of which has been downfaulted beneath the waters of the Pa- 

 cific. It consists of crystalline rocks both igneous and metamorphic and these have 

 commonly been assumed to be of great age — even Archean. This inference of antiquity 

 rests, not upon their known relations, but upon the geosynclinal nature of the Andean 

 seas which are clearly epicondnental and not shelf seas. 



