382 <-"• SKOTTSBERG 



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

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

 not hel|> to get iniphcated. Tiiis idea is by no means new, it has been expressed 

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

 before the Andes were uplifted", as G()(JI) says (lop. 349), but some of these 

 writers did not tr\' to penetrate the complicated geographical-geological history 

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

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

 Ikms(IIi:k (//i') who took pains to inform himself of the history of the Andes 

 as told b\' 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 Tacihc land mass of hypothetical width; one opinion regarded 

 the Coast Range as belonging to this land. Irmscher, who took \\T:c;ener's 

 sitle. did not ask for 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 sufticient to account for uplift and folding. Consequently, he was 

 unwilling to accept Pexck's intrusion theory; if, in the future, it should appear 

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

 which, perha{)s, had been connected with California (p. 45). 



l'i.N( K stellte (lie Aiisbildiint( dor ozeanischen Tiefen am Rande des sudamerika- 

 nischen Kontincntcs, also das \'ersinken angrenzender 'j'eile des Pazifiks, der aufwarts 

 bewegten andinen Scholle gegeniiber und schliesst, dass die niichstliegende Erklarung 

 liir die \'olumenanderungen unter der festen Kruste in dort stattfindenden Massenver- 

 schicbungen zii suchcn ist. Wenn Massen aus der pazifischen Region in die andine 

 iihertrcten, so nuiss in crstcrer 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: 



i)ie ine( hanis( hen Ursachcn des l-altenvorganges sind zweifellos anderer Natur, und 

 (lie .Magniaintnision ist genau so eine Uirkung derselben wie die P'allung. Denn es steht 

 test, dass die ( ichirgshildung niit dem Kmpordringen des Magmas synchron ist und die 

 Intrusion somit gleic hzcitig niit der angcnommenen annuihlichen Lostrennung Siidamerikas 

 von .Atrika. 



Where does the (■iiaigneau-Merriam bank come in.- \Ve(;ener left it unexplained, 

 according to 1)1 Tori it was an "advance foltl". 



l^EKRV and SiN(;i:w.\i,i) (j^), in their review of the tectonic history of South 

 America, describe the develoj)ment in the following terms. 



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

 ( ient massif, the bulk of \\hi( h has been downfaultcd beneath the waters of the Pa- 

 cific. It (onsists of (rystalline ro( ks both igneous and metamorphic and these have 

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

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

 seas which are clearly ej)icontinental and not shelf seas. 



