22 Windhausen — The Cretaceous- Tertiary 



Rio Negro : 1. A portion of the continental Variegated 

 Sandstones, obviously belonging to the upper part of this 

 series. 2. The fault that determines the scarp of these 

 sandstones. 3. The near-shore deposits of mud and sand 

 which lie to the east of the above fault-line and indicate 

 the ancient beach of the Roca-Sea. 4. A peneplain, 

 spread over this old relief, indicating by its imperfect 

 stage but a short period of erosion. 5. The Chichinales 

 Beds, deposited upon this old surface. 6. The later ero- 

 sion of the Rio Negro which first cut down its way in the 

 Chichinales Beds and then advanced deeper into the 

 basal relief. 



It is self-evident that the determination of the age and 

 origin of the Chichinales Beds assumes special impor- 

 tance in connection with the events of earth history 

 which are recorded in the above section. In September, 

 1916, the writer succeeded in finding in the middle hori- 

 zon of these sediments some fragments of Colpodon, 

 Hegetotherium and turtles, also those of a great eden- 

 tate. The thickness of these sediments may be estimated 

 at about 300 feet. Carlos Ameghino, to whom I. am 

 indebted for the classification of these fossil remains, 

 expressed the theory that strata with Notostylops and 

 Pyrotherium might be found below this horizon. This 

 theory is very acceptable for several reasons, as not only 

 a complex of about 120 feet lies under the referred hori- 

 zon with Colpodon etc., but also because the general and 

 lithological character of this lower division of the Chi- 

 chinales Beds bears a great similarity with the classic 

 section that Florentino Ameghino referred to as existing 

 on the southern shore of Lake Colhue Huapi (or Col- 

 huapi), where the strata with Colpodon appear above the 

 strata with Notostylops and Pyrotherium. 53 



Therefore, about Roca as well as in the region of Lake 

 Colhue Huapi observations agree as to the Tertiary age 

 of the alleged mammalian faunas, alike whether the 

 marine Roca and Salamanca Beds, resting at the base of 

 these sections, are correlated with the Upper Cretaceous 

 (Danian) or the lower horizon of the Tertiary. 



The position and determination of age of the dinosaur- 

 bearing horizons and the fixing of their limits towards 

 the top and towards the base is not so clear at present. 

 No doubt the chief deposit of dinosaur bones is found in 



63 Les formations sedimentaires, p. 112, fig. 31. 



