ORIGIN OF OLDEST FOSSILS 
163 
abrupt changes which have transpired when the land faunas and 
floras were established are particularly noteworthy. 
A much earlier and probably an infinitely more important era 
of rapid development in the forms of animal life doubtless oc¬ 
curred immediately after the latter became established on the 
bottom of the ocean. This basic factor was first pointed out by 
the late Prof. W. K. Brooks, something over a generation ago, 
when in scientific circles, life before the Cambric Period was just 
beginning to attract marked attention throughout the world. The 
Brooks essay is one of the master contributions to evolutionary 
philosophy. Although written by one who was not a geologist 
himself, for the contemplation of his paleontological confreres and 
for that reason published in a geological journal, it naturally 
failed to elicit the curiosity it really deserved from earth-students. 
For the same reason it missed its high mission among biologists. 
Despite this circumstance it merits long and deliberate analysis by 
students of ancient organic remains and by geologists, most care¬ 
ful perusal. It severely fixes farthermost limits to oldest fossils. 
Brief review of the circumstances which gave birth to this 
remarkable meditation is not without interest. Possibility of the 
existence of a thick pre-Cambrian succession of sediments was 
occupying the center of the geological stage both in this country 
and the world. Under the title of Algonkian the Federal Geolog¬ 
ical Survey had proclaimed with great eclat the recognition, 
beneath the know Cambric section, of ah entirely new system of 
sedimentary rocks which, it was hoped, would prove to be com¬ 
parable to Murchison’s and Sedgwick’s notable discoveries, half a 
century before, of the Siluria and Cambria in England. 
In this connection the crystalline complex of the Piedmont • 
Plateau, in Maryland, where our zoologist was homed, was under 
especial surveillance. It was fondly expected that some of these 
rocks which had always been considered as among the very oldest 
parts of the Archean massif, if not actually a section of the prim¬ 
eval crust, might prove to belong to the so-called Algonkian sedi- 
mental column. At this very time under the aegis of the Johns 
Hopkins University, at Baltimore, these crystalline schists were 
subjects of intensive study. Some of the results published started 
wide and warm discussion throughout the world. 
With this astounding setting before him, that at the beginning 
of Cambric time biotic types were already so widely and funda- 
