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



in these beds. My own impression was that the different strata 

 on opposite sides of any given water course were remarkably 

 similar and easily identified. Darwin also states, on page 119 

 of his " Geological Observations on South America," that the 

 land in this region has been upraised without the strata having 

 been in a single instance, as far as his observations went, 

 unequally tilted or dislocated by a fault. I think it has now 

 been pretty clearly shown that the transverse valleys of Pata- 

 gonia are due to erosion, and that this erosion was partially 

 accomplished before the deposition of the bowlder formation. 

 The lava beds, which now form opposite cliffs of the same 

 valley, had their origin either during the deposition of the 

 Santa Cruz beds or immediately after, and before any consider- 

 able erosion had taken place ; while those showing conforma- 

 tion with an eroded surface — and there are many such — were 

 ejected long after the close of the Santa Cruz period. 



As an aid to others intending to visit this country for the 

 purpose of collecting fossils, the following suggestions as to 

 localities may be of some service. I have already indicated on 

 the map the most promising localities for fossils in the Santa 

 Cruz beds. I should especially recommend the bluffs on the 

 north side of the Gallegos River from Guer Aike to a point 

 opposite Gallegos ; and the beach, below the bluffs, laid bare 

 at low tide, on the coast between Corriken Aike and Coy 

 Inlet. In the interior there are very promising localities in the 

 bluffs of the Santa Cruz, Chalia and Chico rivers, and over a 

 large area between the last two streams lying directly south of 

 Sierra Ventana. 



Princeton University, Sept. 26, 1897. 



