KI2s^G — GLACIAL A??!) POST-GLACIAL DEPOSITS. 
171 
were considerably eroded by glaciers during tlie close of the Pliocene 
period. 
Before entering on tbe next subject, it is necessary for me to men- 
tion that I wish the greater part of the insertions in the table to be 
taken in an approximate sense ; a few of them, such as " Irish Eound 
Towers," are offered suggestively. 
Remarks on tlie 'Phenomena of the Glacial and Post- Glacial pei'iods 
noticed in the Table. 
The two periods under immediate consideration are strongly dif- 
ferentiated both by their physical and organic features. It is unne- 
cessary to add more to what has already been stated on the former. 
The Glacial period was characterized by the presence of species of the 
genera Elejjhas, Rhinoceros^ and Hippopotamus, doubtless as amply 
protected against a severe frigid climate as the Bear, Walrus, Musk 
Buffalo, Balene Whale, now inhabiting the ice-bound regions of the 
Arctic Circle. The Post- Glacial period appears to have been always 
marked by the absence of the genera above named, at least in the 
area of the British Isles. The shells special to the glacial period are 
such as still inhabit the Arctic seas : a few, but very few, may have 
become extinct. Whether any new species have come iuto existence 
during the Post-Glacial period is a question whit-li I am unable to an- 
swer; but it would appear that a few are special to this term, if we 
confine our observations to the British and adjacent seas, — the fol- 
lowing species, Lima excavata, Haliotis tuherculata, Fastis Berniciensis, 
and Litorina litoralis, bt-ing unrecorded in Glacial and Pliocene de- 
posits. The genus Homo belongs to both the glacial and post-glacial 
period : it was represented as early as the close of the subaqueous 
epoch or the beginning of the second subaerial division of the Glacial 
period by a low form or extinct species, — a view strongly countenanced 
by the Neanderthal skeleton, as well as the rudely-chipped flint-imple- 
ments occurring in the elephant gravels of Amiens, lloxne, and other 
places. Probably a higher type existed at the same time, as indicated 
by the skulls found in the Engis caves near Liege. The " Borreby 
people " of the Post-Glacial period appear to have descended from the 
JN'eauderthal race. How far back in geological time it was that the 
genus nvdde its first appearance on our planet is a question yet to be 
solved. There is no reason, however, to doubt tliat it was repre- 
sented by species during the Pliocene, or even the Miocene period. 
The line of demarcation between any two epochs, also between 
the Glacial and Post-Glacial periods, I assume as being formed by 
terrestrial and oceanic conditions corresponding to the present re- 
lative level of laud and sea. 
Glacial Period. 
First (subaerial) epoch. — The elevation of the British area, although 
the laud is assumed to have been thirteen hundred feet (=220 
fathoms) higher than it is at present, is not, in my opinion, to be 
regarded as the cause of the severe climatic conditions of this epoch. 
