28 
ORGANIC DEPENDENCE AND DISEASE 
study; it is too soon to determine its value and to discuss 
it here is inappropriate, but we must at least grant to these 
suggestions the probability that we have heretofore greatly 
underestimated the time required for the upbuilding of the 
fossiliferous rocks and for the evolution of life. In terms 
of millions of years time becomes incomprehensible and the 
sum total, whatever it may be, must be regarded as com- 
petent for all the evolutionary processes of life and work. 
INDEPENDENCE OF THE FIRST FAUNA 
We still stand in ignorance of the real primitive or in- 
ceptive fauna of the earth, and when we use the expression 
4 4 first fauna,’ ’ it is with the reservation which absence of 
facts compels. We may speak freely, however, of the first 
fauna known to us and with a fulness of knowledge that 
justifies, in good measure, deductions regarding the nature 
of its ancestors upon earth. The fauna of the Cambrian 
system represents to us the actually known first fauna, for 
evidences of organic life in the rocks before and below 
the Cambrian are desultory though positive. While we are 
considering the special nature of the Cambrian fauna from 
the point of view we have here taken, let it be not forgotten 
that this so-called 4 4 first fauna” must have been millions 
of years in the making, worked out by the slow and arduous 
advances with which first steps have ever been taken in the 
course of nature. Our 4 4 first fauna,” then, is also the prod- 
uct of the ages ; and in spite of its complexion of simplicity, 
the entire absence in it of the vertebrate type and of what 
we are wont to regard the more progressed of its inverte- 
brate types, specialization in anatomical structure is per- 
haps, in view of our expectations, the most obvious fact that 
it sets forth. Let us keep this important fact in mind as we 
study its composition with reference to independent and de- 
pendent life. 
