NEWER PLIOCENE PERIOD. [Ch. VI. 



No. 9. 



Section of calcareous yrit and pcperino^ cost of Patagonia. South tide of pass* 

 Vertical height about thirty feet. 



No. 10. 



Section of the same beds on the north side of the pass. 



The disposition of the strata, on both sides of the pass, is most 

 singular, and remarkably well exposed, as the harder layers 

 have resisted the weathering of the atmosphere and project in 

 relief. The sections exhibited on both sides of the pass are 

 nearly vertical, and do not exactly correspond, as will be seen 

 in the annexed diagrams (Nos. 9 and 10). It is somewhat 

 difficult to conceive in what manner this arrangement of the 



O 



layers was occasioned, but we may, perhaps, suppose it to have 

 arisen from the throwing down of calcareous sand and volcanic 

 matter, upon steep slanting banks at the bottom of the sea, in 

 which case they might have accumulated at various angles of 

 between thirty and fifty degrees, as may be frequently 'seen in 

 the sections of volcanic cones in Ischia and elsewhere. The 

 denuding power of the waves may, then, have cut oil' the upper 



