J. B. Hatcher — Geology of Southern Patagonia. 345 



this region increase in thickness as we proceed southward 

 along the coast, and appear first toward the north capping the 

 summits of the higher table lands, then farther south they are 

 brought to the water's level by a slight southeasterly dip, and 

 finally, still farther south, they entirely disappear beneath the 

 sea. 



In discussing the age of these marine beds Dr. Ameghino 

 refers them to the Miocene because they contain oysters " of 

 large size and of a species similar to that characterizing the 

 Santa Cruz formation." Prof. Henry A. Pilsbry, who has 

 studied our first collections from these beds and already pub- 

 lished in the Proc. of the Phil. Acad, of Sci. a list, with 

 descriptions of new species, refers these beds to the Pliocene. 

 He has furnished me the following list of species : Trojphon 

 laciniatus Martyn, T. inornatus Pilsbry, Calyptrcea niammil- 

 laris Brod. (?), Turritella innotabilis Pilsbry, Cardium sp. 

 indet, Pecten actinodes Sowb., Ostrea ferarresi Orb.,* O. n. 

 sp., Pinna sp. indet., Magellania venosa Sol. Of these he 

 remarks " Trophon laciniatus, Magellania venosa and the 

 Calyjvtrcea are living species. The Cardium and Pinna may 

 also be living. The others are extinct, but the Turitella is 

 closely allied to a living Chilian form." We have since sent 

 Dr. Pilsbry additional material which will enable him to nearly 

 double the list of species, and which, he says, only confirms 

 the Pliocene age of the beds. 



The Tehuelche or Shingle Formation. — The presence of the 

 Cape Fairweather beds with an abundant marine fauna, above 

 the Santa Cruz beds, is positive proof of the submergence of 

 this region. That this submergence took place long after the 

 close of the Santa Cruz period can, I think, be well demon- 

 strated, for, as shown in fig. 6, the Cape Fairweather beds are 

 seen to rest upon the eroded surface of the Santa Cruz beds. 

 This unconformity by erosion cannot be considered as due to a 

 secondary deposition of the materials of the Cape Fairweather 

 beds on the surface of the slope of the canon where the sec- 

 tion was made, for the two strata of bowlders and sandstones 

 are here quite distinct, and show no mingling of materials, 

 such as would have resulted from secondary deposition. More- 

 over the same unconformity is observable a little farther north 

 in a section exposed for a long distance and where an abso- 

 lutely level plain prevails above, as shown in fig. 7. 



From these facts and others to be mentioned later, I con- 

 clude that after the deposition of the Santa Cruz beds and 

 prior to the deposition of the Cape Fairweather beds this 

 region was for a considerable period above sea level and sub- 

 jected to erosion ; during this period of erosion all the more 



* In regard to the identification of the large oysters of Patagonia see paper by 

 Dr. A. E. Ortmann in this number of this Journal, p. 355. 



