288 PATAGONIAN EXPEDITIONS : PALAEONTOLOGY. 



Ihering (1897, P- 34^) rnakes the " Patagonian formation" Upper 

 Eocene, the " Suprapatagonian " Oligocene or Lower Miocene, while Coss- 

 mann (1898, p. no) in reviewing v. Ihering's paper says that the "Santa- 

 cruzian" formation has rather a Miocene than an Oligocene character. 



Dall (1898 b, p. 342) having received "Santa Cruz" fossils from v. 

 Ihering, says that these beds, if not Miocene, can hardly be referred to a 

 horizon older than Oligocene. 



Ameghino finally (1898-1899) places the Patagonian and Suprapata- 

 gonian beds in the Upper Cretaceous and Lower Eocene. 



Our own studies have convinced us, that the age assigned to these 

 beds by Ameghino and Mercerat is certainly too great. In his first pub- 

 lication (1897) Mr. Hatcher was still under the influence of Ameghino's 

 views, but he already tried to move up the series in the scale, making the 

 Patagonian beds Eocene, and the Suprapatagonian beds Miocene. In the 

 later publication (1900) he unites both, and makes them according to 

 the evidence furnished by the present writer Miocene. 



In the following I shall try to prove in detail my opinion that these 

 beds are of Miocene age. 



I wish first to say a few words on the method employed. In very many 

 cases the age of Tertiary deposits is determined by the percentage of liv- 

 ing species found in them. In my opinion this line of evidence is entirely 

 inadmissible in our case, and I hardly need to say anything to support 

 this view : this method may be safely used in Europe, but in the southern 

 hemisphere it is out of the question. 



For the sake of completeness, however, we shall state here the percent- 

 age of living forms in the Patagonian beds. 



Von Ihering gives (1899, p. 38) 6 species out of 70, that is to say, 

 8-9 per cent. 



1. Trochita cornigata (Infundibulum c.~). 4. Siphonalis cf. nodosa. 



2. Trochita magettanica (Infundibulum cly- 5. Trophon laciniatns ( T. patagonicus). 



peoluni). 6. Magellania globosa (M. lenticularis). 



3. Siphonalia dilatata (S. domeykoana). 



divisions are certainly all wrongly identified ; in fact, the succession of the forms has been almost 

 inverted. Ostrea patagonica is not found at all in the Patagonian beds"; 0. fcrrarisi (which is only 

 the young of 0. patagonica) has never been found in Santacruzian beds, and 0. torresi has never 

 been found in the Tehuelche beds. The exact stratigraphical position of these oysters is given 

 above. The idea of characterizing five horizons exclusively by the oysters found in them, shows 

 that Mercerat seems to be very innocent of Palaeontology. 



