THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Art. I. — The Problem of the Cretaceous-Tertiary Bound- 

 ary in South America and the Stratigraphic Position 

 of the San Jorge-Formation in Patagonia; by A. Wind- 



hatjsen, Buenos Aires. 



Contents. 



Introduction : The Cretaceous-Tertiary problem in North and South America. 



Part I: Origin and history of Patagonian molluscan faunae. Ant- 



arctica as a center of evolution for marine and terrestrial 

 faunae during the Cretaceous and Tertiary. The question 

 of age, stratigraphic position and general faunistic character 

 of the San Jorge-Formation. 



Part II: Stratigraphy of the San Jorge-Formation. Stratigraphic 



limits. Critical review of the exposures and sections in 

 geographical order from north to south. The strata at the 

 bottom and top of the marine San Jorge: Dinosaur-bearing 

 Pehuenche Beds and the .pediments with the ancient Pata- 

 gonian mammal-fauna, the Notostylops, Astraponotus and 

 Pyrotherium Beds (Casamayor and Deseado). 



Part III: Paleogeography of the San Jorge-Formation. Reconstruc- 



tion of the shore-lines of the San Jorge-Sea. The great 

 depression between the ancient Patagonian continental plat- 

 form and the structural elements of Central and' Northern 

 Argentina. Characteristic features of sedimentation. 



Part IV: Paleontology of the San Jorge-Formation. Critical exami- 



nation of the faunistic characters. The transgression of the 

 San Jorge-Sea as a forerunner of the Patagonian Formation. 

 Age of the San Jorge and position of Pehuenche and 

 mammal-bearing horizons. 



Conclusions. 



Appendix : Table of the invertebrates found in the San Jorge at different 

 localities. 



Introduction. 



Critical treatment of the problem of the Cretaceous- 

 Tertiary boundary has not yet led to conformity of 

 opinions. It was, however, a necessary prelude to sum- 



Am. Jour. Sci.— Fourth Series, Vol. XLV, No. 265. — January, 1918. 



