reached. We need in that 
case no longer fear that we 
may soon reach a Mars-like 
condition, when the greatest 
care is necessary to conserve 
the water-supply. We need 
not feel apprehensive lest we 
are fast racing towards a con- 
dition such as we see in our 
own satellite—the moon. We 
shall not die of refrigeration. 
One authority goes so far as 
to say that our radio-active 
substances will not only pre- 
vent that, but may actually 
bring about the danger of 
such heat as will possibly 
result in catastrophic action 
of the earth’s surface. It is 
strange, indeed, that all the 
activities of human life are 
carried on at the surface of so 
Marvels of the Universe 867 
Phoio by] (Mrs. Aubrey le Blond. 
In this—the Aletsch—Glacier there is a central moraine of rock-debris which has 
flowed down from the mountains, and is deposited with boulder-clay on the lower 
grounds, where the glacier melts. The valley is scored with striations caused by 
blocks imprisoned in the ice. 
thin a crust, and stranger that we still know so little of what is going on more than a mile from 
the surface. 
We have already described what an unconformity is. Such an one as occurred between the 
Archean and the Algonkian again appears now at the bottom of the Cambrian rocks. An immense 
length of time must have elapsed before these came to be laid down upon the upturned edges 
of the Algonkians. With the 
Cambrians we can turn to 
those more familiar British 
areas where the rocks were 
first noticed and studied. But 
what we cannot see in Britain 
are the clear and _ distinct 
evidences which appear in 
Norway and in far-off China 
of an Ice Age having actually 
occurred before they came to 
be laid down. The Cambrians 
give us clear evidence that the 
forces of nature which we see 
going on around us now were 
then fully in evidence also. 
Rains and frosts, winds and 
water-action carved out the 
land into hill and dale. Above 
the Cambrian rocks we find 
next the Ordovician, and above 
that the well-known Silurian 
Photo by] [C. A. Byers. 
This view of the Great Canon illustrates the gradual lowering of the upland plain 
by the carving of the river through the rocks, which were subsequently degraded by 
atmospheric agencies. 
