864 Marvels of the Universe 
Keewatin rocks there is so much carbon that it is probable that at least seaweeds had begun 
to grow. 
Above these rocks, in the same Great Canon, there rests another great formation, the Algonkian, 
and this in some places is itself scores of thousands of feet thick. Nor was it deposited uniformly 
on the Archean. The latter masses had in the interim become raised out of the sea or out of 
reach of great volcanic influences, and had formed possibly a part of a continent. Denudation 
of its surface had planed away much of its irregularities, and the crumplings and contortions 
were scarcely visible. We 
cannot tell how long this old 
land-surface lasted. We only 
know that in the course of 
time it underwent the rigours 
of an Ice Age, before it went 
down beneath the sea again, 
and on its planed-down edges 
the great Algonkian series was 
laid down unconformably. In 
the Great Canyon there are 
no less than twelve thousand 
feet of these rocks, which are 
themselves divided about half- 
way by a great unconformity, 
and contain several sheets of 
lava interbedded with them. 
The two great formations 
which we have mentioned 
were formerly known as the 
Laurentian system, and they 
cover an area which is esti- 
mated at two million square 
miles. In Britain the rocks 
we have been dealing with 
are represented by the Lewi- 
sian gneisses of the Hebrides 
and the Torridonian of Scot- 
land. 
In passing on to the well- 
Photo by] [R. Welch. 
; : recognized Cambrian rocks, 
Old Red Sandstone boulder supported oa a pillar of rock at Kenmare, Kerry. The 
boulder has protected the pillar from denudation, whereas the surrounding rock has | We reach a time when Mother 
disappeared. Earth had to some extent 
settled down from the early and impetuous days of her hot youth. If the rocks we have dealt 
with were now piled upon one another, and a further series were piled on the top of these, repre- 
senting a length of time about equal to all that had gone before, we should have a towering 
cliff about fifty miles high. In imagination we might see a picture something like that shown in our 
coloured illustration. But in real fact this exists nowhere. At no place are all the formations to 
be seen together. But the sequence is one which is never departed from. The order is always the 
same. The base of the Archean has never been seen, and it probably stretches at varying distances 
below every formation on earth. It is the bottom of what has come to be known as the Crust of 
the Earth, and this has been put by varying authorities of recent years at between twenty-five and 
