290 
PATAGONIAN EXPEDITIONS : 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. 
Cretaceous. 
Eocene. 
Oligocene. 
Miocene. 
Pliocene. 
Recent. 
1. Cidaris 
ant-arctica 
2. Toxop- 
C. avenion- 
ensis, 
Europe 
Genus Tox- 
neustes 
opneustes 
praecursor 
3. Scutella 
S. subro- 
Echinarach- 
patagonen- 
tunda, 
nius mira- 
sis 
Cyrtoma 
Europe 
bilis, Japan 
4. Cyrtoma 
posthu- 
India, 
mum 
Europe 
