179 
destroying land life^if, indeed^ any escaped the glacial conditions. 
And I would here remark that it does not require the intense 
cold of an Arctic climate to destroy a tropical fauna. Darwin 
sees this in the case of the flora^ and says that it is difficult to 
understand how the tropical productions could have escaped 
entire annihilation. In the fourth edition of the Origin of 
Species he says^ I had hoped to find evidence that the tropics 
in some part of the world had escaped the chilling effects of 
the Glacial period, and had afforded a safe refuge for the suffer- 
ing tropical productions ;* but, up to the time of his writing 
the fifth edition, he looked in vain for that refuge. If the 
tropical flora was annihilated, there remained a poor chance of 
survival for the tropical fauna. Without the care of man a 
tropical fauna would not, at the present time, live through 
many winters in the valley of Chamounix, and in that valley 
the glaciers do not come so near to the sea level as did the 
glaciers in Nicaragua and at San Dafael in the Glacial period, 
according to the evidence of the late Thomas Belt, who had 
made glaciers a part of his study. 
26. All the geolgical evidence we possess relating to that 
period points to conditions that would render almost inevi- 
table a break in the continuity of mammalian life, whilst the 
hypothesis of Charles Darwin requires that there should be 
no break, but that the present fauna should be the continua- 
tion of the older fauna with but slight modifications in the 
course of descent. 
27. Gradual migration of the fauna southward as the in- 
creased cold came on has been suggested as a possible escape of 
the land life ; but this would be very partial, for the mountain 
barriers, owing to the accumulation of ice and snow, would be 
much more formidable than they are now, and this southern 
migration would be impossible where submergence had com- 
menced. The low lands would go first under water, and the 
natural retreat of the fauna would have no reference to points 
of the compass, but an ascent from time to time as the waters 
encroached ; the subsidence still going on, the hills would 
eventually become islands. Ultimately, the lower hills would 
be covered with water, and the higher ranges would bring 
their glaciers to sea level, when they would be floated off as 
icebergs. Dr. James Croll remarks that where proper ob- 
servations have been made we are forced to the conclusion 
that the connexion between glaciation and submergence is 
not accidental, but the result of some fixed cause, — that they 
* Origin of Species, 4th edition, pp, 448, 450. 
N 2 
