iS 77-J Southern Hemisphere . 333 
animals, has given an excellent summary of the facts known 
respecting these lost animals, and has placed the question 
of their extinction before us with clear-cut distinctness.* 
He shows that in very recent geological times a great 
change has taken place in the fauna not only of South 
America, but of North America and Europe, and that this 
change is unprecedented in older geological periods. We 
now live, he says, “ in a zoologically impoverished world, 
from which all the hugest and fiercest and strangest forms 
have disappeared.” He urges, with luminous force, that 
there must have been some physical cause for this great 
change, which must have added at the same time over large 
portions of the earth’s surface. Such a cause he considers 
is to be found in that great era, the glacial period. 
There is much to be said in favour of Mr. Wallace’s con- 
clusion. The Pampean mud occifpies the same relation to 
recent deposits as other clays whose glacial age has been 
satisfactorily determined. Both it and the gravel-beds of 
Patagonia, in many places, lie diredtly above marine depo- 
sits of undoubted late Pliocene age, as they contain shells 
of Ostrea Patagonica. They hold, therefore, the same posi- 
tion between the tertiary and recent deposits that glacial 
beds occupy in other countries. The Patagonian deposits 
also contain large boulders that have been transported from 
the Cordillera. 
The Pampean mud has been compared with the loess of 
the Rhine-— a similar fine slightly-indurated clay, which 
contains the bones of the extindd mammoth and woolly 
rhinoceros. It appears to be still more like the beds of 
diluvial clay that form the wide-spread steppes of Southern 
Russia. This clay is of undoubted Glacial age, and when 
traced northward contains large blocks of stone derived 
from rocks hundreds of miles to the north, just as the Pam- 
pean mud when traced southward is replaced by gravel-beds 
with boulders from the Cordillera. In the January number 
of this Journal I have advocated the theory that the diluvial 
clays of Northern Europe and the loess of the Rhine and 
the Danube were spread out in a great lake, when the bed 
of the Atlantic was occupied by ice that stopped the drainage 
of Europe as far as it extended. In eastern North America 
there is evidence of a similar interruption to the drainage 
of the continent to at least as far as North Virginia. 
It is a remarkable fadt that to about as far from the South 
Pole in South America as from the North Pole in North 
* Geographical Distribution of Animals } vol. i., p. 143. 
