CLIMATES OF GEOLOGIC TIME—SCHUCHERT. 291 
vast mass more than half (50,286 feet) is either pure limestone, 
magnesian limestone, or dolomite, and single beds are known with 
a thickness of 1,500 feet. Certainly so much limestone represents 
not only a vast duration of time but also warm waters teeming with 
life, almost nothing of which is as yet known. There is further evi- 
dence of life in the widely distributed graphites, carbon derived from 
plants and animals, which make up from 3 to 10 per cent by weight 
of the rocks of the Adirondacks. (Bastin, 1910.) The graphite 
occurs in beds up to 13 feet thick, and at Olonetz, Finland, there is an 
anthracite bed 7 feet thick. 
It is also becoming plain that there was in the Proterozoic a very 
great amount of fresh-water and subaerial deposits, the so-called 
continental deposits, some of which indicate arid climates. Because 
of the apparent dominance of continental deposits and the great 
scarcity of organic remains throughout the Proterozoic, Walcott has 
called this time the Lipalian era (1910). 
We have seen that the Proterozoic began, with a glacial period, as 
evidenced by the tillites of Canada, but that this frigid condition 
did not last long is attested by the younger Lower Huronian lime- 
stones of Steeprock Lake, Ontario, having a thickness of from 500 
to 700 feet and replete with Atikokania, sponges up to 15 inches in 
diameter, and forming reef limestones several feet thick, found there 
by Lawson and described by Walcott (1912). This discovery is of 
the greatest value, and opens out a new field for paleontologic 
endeavor in Proterozoic strata and for philosophic speculation as 
to the time and conditions when life originated. 
We have also seen that the Proterozoic closed with a frigid climate, 
as is attested by the tillites of Australia, Tasmania, and possibly 
China, while the other glacial deposits of India, Africa, Norway, and 
Keweenaw certainly do in part indicate another and older period of 
cool to cold world climates. 
Cambric—Due to the researches of many paleontologists, but 
mainly to those of Charles D. Walcott, we now know that the shallow- 
water seas of Lower Cambric time abounded im a varied animal life 
that was fairly uniform the world over in its faunal development. 
It was essentially a world of meduszx, annelids, trilobites, and brach- 
iopods, animals either devoid of skeletons or having thin and nitrog- 
enous external skeletons with a limited amount of lime salts. The 
“lime habit”? came in dominantly much later; in fact, not before the 
Upper Cambric. However, that the seas in Lower Cambric time 
had an abundance of usable lime salts in solution is attested by the 
presence of many Hyolithes, small gastropods and brachiopods, and 
more especially by the great number of Archzocyathine, most 
primitive corals, which made reefs and limestones 200 feet thick 
and of wide distribution in Australia, Antarctica, California (thick 
