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



From the high angle of inclination of the Supra-Patagonian 

 beds all along the eastern base of the mountains, it is evident 

 that at the close of that period there were great orographic 

 movements throughout southern South America. Not only 

 were the Cordilleras greatly elevated, but also the region to 

 the eastward, far beyond the present limits of the Atlantic 

 coast, was brought above sea level. The eastern border of this 

 great land mass was perhaps not far to the eastward of the 

 Falkland Islands, and may be approximately represented by 

 an imaginary line connecting these islands with certain out- 

 lying bodies of Primary Pock at Port Desire, and other places 

 farther north, and perhaps extending also in a southeasterly 

 direction as far as South Georgia Island. The great develop- 

 ment of the Santa Cruz beds along the coast, especially between 

 the Coy and Gallegos Pi vers, as well as the very shallow 

 nature of the water between that coast and the Falkland 

 Islands, are both important evidences of a much greater east- 

 ward extension of the land during the Santa Cruz period than 

 at present. 



Consequent upon the elevation which took place at the close 

 of the Supra-Patagonian period, there was between the borders 

 of the old land-mass, now represented on the east by the Por- 

 phyries of Port Desire, and by the Falkland Islands ; and on 

 the west by the Cordilleras, a depression, in which were laid 

 down the fresh-water, lacustrine deposits, now known as the 

 Santa Cruz beds, and containing one of the richest and most 

 varied vertebrate faunas known. That the Santa Cruz beds 

 •are of fresh-water origin rather than marine is shown by the 

 diatoms. It is also clear from the nature and composition of 

 the strata, that they were not deposited in a great, continuous 

 lake, but rather in a low, flat, marshy country with smaller 

 lakes and connecting water courses. As evidences of this I 

 would cite the numerous examples of cross-bedding, and the 

 fact that the beds of sandstones, clays and conglomerates 

 continually replace one another, both of which facts are well 

 shown in tig. 6 at G and J, and in figures 10 and 11. 



The Santa Cruz beds may be separated, according to the 

 vertebrate remains found in them, into an upper and lower 

 horizon. The strata of the lower Santa Cruz beds, as com- 

 pared with those of the upper, are of a lighter color, more con- 

 tinuous and are composed of finer materials, containing few or 

 no conglomerates. They are best displayed in the bluffs of 

 the Santa Cruz, and of the upper Chalia and Chico Rivers, 

 where they are characterized by the great numbers of herbiv- 

 orous marsupials and gigantic birds found in them. The 

 upper Santa Cruz beds are best exhibited in the bluffs of the 

 sea and the Gallegos River from Coy Inlet to Guer Aike, 



