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PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 



with Patagonian species, and thus it seems impossible to compare 

 directly the Patagonian beds with any deposit of the northern hemisphere. 



Nevertheless, the comparison with northern faunas proves to be very 

 valuable. As we shall see below, although we hardly find an identical 

 species, quite a number of forms show close affinities to northern species. 

 This method was used by Moericke (1896) for the Navidad beds of Chili, 

 and he concluded that these beds are possibly Miocene, since a number 

 of species show distinct relationship to Miocene species of the northern 

 hemisphere, and since these relations are the prevalent ones. 



Although it might be objectionable to draw a conclusion like this, when 

 only a few species are known, it is quite another thing when the bulk of 

 the species available for comparison points the same way. Indeed, it is 

 quite possible that closely allied species are found in deposits of different 

 age, and it is not admissible to rely on single instances of this kind. But 

 when as is the case in our material a large percentage of the whole 

 fauna, and a still larger one of those species which may be compared at 

 all with known ones, shows the identical relations to northern forms, it is 

 safe to say that this is a possible way to ascertain the age of any deposit, 

 and, as it happens, this is the only way left in our case. 



Therefore I have used this method in the first place, and have found 

 that the affinities of most of the Patagonian species point to a Miocene 

 age of these deposits. This conclusion will be strengthened by other 

 considerations to be made below. 



First I shall give here a table containing only those species which 

 permit a comparison with species of the northern hemisphere. 



