RISE AND FALL OF PATAGONIA I3I 



"Guarantic," and considered to be Middle to Upper Cre- 

 taceous. He seems to consider them mostly land deposits 

 because in them have been found dinosaur bones, and 

 because they so generally have fossil wood; in describing 

 which last Ameghino even goes so far as to state that in 

 these petrified forests the trees are often standing where 

 they grew. We never saw any wood in such a position that 

 it could be standing where it grew, and indeed its very 

 position and distribution seemed to mark it for drift wood, 

 while the occasional beds with marine shells confirmed my 

 belief that the beds were all marine, and apparently of 

 Upper Cretaceous age. 



Toward the end of the Cretaceous or during the early 

 Eocene these beds were raised to low-lying land, and the 

 Eocene epoch is only represented by the break or uncon- 

 formity between these beds and the overlying Patagonian 

 ones. During this time of elevation such rivers as coursed 

 over or through these low lands, made small deposits in 

 their beds or on the adjacent flood plains, in which natu- 

 rally were buried the bones of such animals as died in 

 or near the stream. These deposits therefore form pockets 

 in the upper part of the Guarantic though of later age. 

 It is these which have been termed Notostylopus and 

 Pyrotherium beds, always limited in extent and of but in- 

 frequent occurrence. Their age may be anything from 

 Early Eocene to late Oligocene, its exact time only to be 

 determined by the contents- of the beds, and as these are 

 totally unique the determination is largely a matter of 

 judgment. Our pocket on the Chico River is in this class. 

 It is clearly later than the Notostylopus beds as the ani- 

 mals are much more specialized. The animals of the 

 Pyrotherium beds have many affinities with those of the 

 Santa Cruz above the Patagonian. The time necessary 

 to lay down the 600 to 1,000 feet of the Patagonian beds 

 would fully account for such changes as we find, and there- 

 fore I feel confident that these Pyrotherium beds should 



