68 THE NEOG^IC REALM. [CHAP. 



on the river of that name, but likewise further north in the Chubat 

 district. These Santa Cruz beds are exceedingly rich in mamma- 

 lian remains, which are stained of a deep black colour ; and while 

 they contain many groups common to the Pampean formation, 

 they lack those forms found in the latter which have an Arctogseic 

 fades, thus indicating that we have reached an epoch when the 

 fauna of South America was far more completely isolated from 

 that of the rest of the world than is at present the case. By Dr 

 Ameghino the Santa Cruz beds were at first correlated with the 

 lower Eocene of Europe, although he subsequently admitted that 

 they must occupy a somewhat higher position in that period 1 . 

 From the nature of their entombed mammals 2 it is, however, 

 certain that they must be still newer, and they cannot be regarded 

 as older than lower Miocene. Indeed, they are underlain by the 

 so-called Patagonian beds 3 , which are of marine origin, and 

 contain numerous cetaceans, among which are whalebone whales 

 (Mystacoceti). From equivalent beds in the Chubat district of 

 Patagonia, a large number of such cetaceans have been described 

 by the present writer 4 , and it is quite evident that the oldest age 

 that can be assigned to these beds is upper Oligocene, seeing that 

 in Europe whalebone whales are unknown till a considerably later 

 epoch. Probably the freshwater beds containing the peculiar 

 mammal alluded to below under the name of Pyrotherium are the 

 freshwater equivalents of the Patagonian horizon 5 . 



Additional evidence in support of the comparatively late age 

 of the Patagonian beds is afforded by the researches of Prof. Cope 6 

 on the cetaceans of the Miocene (or Upper Oligocene?) of the 

 United States. From these beds have been obtained remains of 

 Hypocetus (Paracetus) a genus elsewhere known only from the 

 Patagonian beds together with Cetotherium (also occurring in the 

 latter deposits), Balcenoptera, and a species of Balcena identified 

 with one from the European Pliocene ; the North and South 

 American species of Hypocetus being closely allied. 



1 Bol. Ac, Cordoba, Vol. xin. p. 260 (1894). 



2 Remains of the existing genus Dasypus occur in these beds. 



3 Ameghino, loc. cit. 



4 Ann. Mus. La Plata, Pal. Argent. Pt. II. (1893). 



5 Ameghino, op. cit. p. 262. 



6 Prof. Amcr. Phil. Soc. Vol. XXXIV. pp. 135 155 (1895). 



