CONCLUDING REMARKS. 201 
test these terms “Quaternary,” or “ Post-Tertiary,” by such a standard as that 
of the reference of those beds in which species not known living occur to the 
“Tertiary” group, and of those beds which contain none but living species to the 
“Quaternary,” the standard will vary accordmg to what forms of life we select. If 
we take the Mollusca, we find that a proportion of them not known as living occur 
in the Lower and Middle Glacial sands, and that, even in the Bridlington Bed, there 
are two such; so that if the division between Tertiary and Quaternary were based upon 
Molluscan evidence, we should have to draw the line just above the Bridlington horizon 
and below that of the Scotch beds, for in the Scotch none but species still living on 
‘one side or other of the Atlantic are found. If, instead of this, we take the Mammalia, 
the line would have to be brought down to that much later period when the 
Macharodus and the extinct species of Hephant, Rhinoceros, and Hippopotamus died out. 
‘On the other hand, if the Quaternary or Post-Tertiary age were attempted to be made 
co-ordinate with the existence of man, we should not only be placing it in the most 
uncertain of all positions in consequence of our knowledge of the evidences of man’s 
existence undergoing almost daily extension, but the line so regulated would differ equally 
from that based on the Molluscan evidence, and from that on the higher animals; the 
evidence yet obtained of man’s existence not going back to those later glacial formations 
in which the Mollusca belong to species which are all living, but showing him, 
nevertheless, to have long existed coevally with the extinct Mammalia. 
While this difficulty of making any consistent definition of the term is so obvious, we 
have, on the other hand, from the Older Crag upwards evidence, in the case of the 
Mollusca at least, of the most gradual transition from a period treated by all as Tertiary, 
when a considerable proportion of the species consisted of forms not known living, to the 
most recent beds in which the included remains, to whatever part of the animal kingdom 
they belong, are all those of living species. 
I have therefore referred all formations anterior to the recent, to the Tertiary period,—a 
period which by long custom has become well known, and must, until our knowledge 
becomes extended, be retained as convenient ; and which, in Hurope at least, appears to 
be sharply defined by unmistakeable physical and paleontological features, though even 
in this quarter of the world future discoveries may not improbably eventually necessitate 
its abandonment. 
At the end of the synoptical list which follows, the change which has taken place 
through the formations succeeding the Coralline Crag, from the Mediterranean aspect 
which the Mollusca of British seas possessed at the period of that Crag, is pointed out. 
