THE SILUKIAN BEACH. S3 
The statement that different sets of animals 
and plants have characterized the successive 
epochs is often understood as indicating a dif- 
ference of another kind than that which distin- 
guishes animals now living in different parts of 
the world. This is a mistake. They are so- 
called representative types all over the globe, 
united to each other by structural relations and 
separated by specific differences of the same kind 
as those that unite and separate animals of differ- 
ent geological periods. Take, for instance, mud- 
flats or sandy shores in the same latitudes of 
Europe and America ; we find living on each ani- 
mals of the same structural character and of the 
same general appearance, hut with certain specific 
differences, as of color, size, external appendages, 
etc. They represent each other on the two conti- 
nents. The American wolves, foxes, bears, rab- 
bits, are not the same as the European, but those 
of one continent are as true to their respective 
types as those of the other ; under a somewhat 
different aspect they represent the same groups 
of animals. In certain latitudes, or under condi- 
tions of nearer proximity, these differences may 
be less marked. It is well known that there is a 
great monotony of type, not only among animals 
and plants, but in the human races also, through- 
out the Arctic regions ; and some animals charac- 
teristic of the high North reappear under such 
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