GRAND DISCOVERIES OF LIFE 
5 
ity, hardship, and fierce struggle for existence. Forms grew 
larger. Certains ones sustained themselves to the disadvantage of 
others. These were then able to turn their energies to growth 
and reproduction. Strong competition on the sea bottom or to¬ 
wards the shore soon gave rise to variant types, many of which 
persist to the present day. 
With the further occupation of the clear, shallow, epicontinental 
seas hard parts developed and gave strong impetus to greater 
diversity. It is, then, not now so surprising as it once was that 
Cambric life should burst forth in such boundless profusion. At 
that time the span of evolution was already twice or thrice as long 
as from the beginning of the Cambric age to the present time; 
perhaps somewhat longer but certainly not eight to ten times 
longer as often surmised. Already hard parts of organisms, de¬ 
veloped far down in the pre-Cambric column were unearthed 
lately beneath even the horizon of the once famed but mystical 
Eozoan. 
As Brooks astutely remarked, we are not to think of the popu¬ 
lating of the bottom of the sea as a physical problem, but as a 
discovery and colonization, very much like the colonization of 
islands. This first bottom life was not pelagic life approaching 
the shore and occupying the littoral, because there the sediments 
were highly detrimental to such life. It was far enough from the 
coast for the waters to be free from sediments and deep enough for 
the pelagic food supply above it to develop without restriction. 
It was the deep zone around the islands and continents. 
The first faunas which became established in this deep zone 
may have been the ones which persisted through the ages and the 
ones which may have given rise to modern animals. At all events, 
this deep zone was the birth place of the fauna which has survived, 
and it was the ancestral home of all the higher metazoa. After 
the foundations of the bottom fauna were laid it must have become 
very difficult for new forms to establish themselves. Thus evolu¬ 
tion proceeded along lines which resulted in elaboration and 
specialization of the types already early established rather than 
through the introduction of new branches. The great groups of 
animals were rapidly developed from pelagic forms. They in¬ 
creased in size and developed hard parts. This was, indeed, 
perhaps the most important step in all organic evolution. 
The sudden bursting forth at the beginning of Cambric time of 
