32 NEW YORK STATE MUSEUM 
ocean was thousands of feet deep when the deposition began, be- 
cause there may well have been a gradual subsidence of the sea floor 
during the process of sedimentation, which means that there was 
not necessarily very deep water at any time. In fact, the very 
character of the sediments clearly indicates that the Grenville ocean 
was, for most part at least, of shallow water, for such sediments as 
sands and muds have rarely if ever been carried far out into an 
ocean of deep water. The great ocean abysses of today are not re- 
ceiving any appreciable amount of land-derived sediments. Hence 
it is practically certain that the very ancient Grenville sea bottom 
gradually settled as the sediments accumulated. Similar phenomena 
are definitely known to have occurred in many later basins of 
deposition. 
The reader may naturally be disposed to ask, How long ago did 
the Grenville ocean exist? There are grave difficulties in the way 
of answering this question in terms of years, as we have nothing 
like an exact standard of this kind for comparison. While it is fully 
recognized that not even approximate figures can be given, a very 
conservative statement would ascribe an age of twenty to twenty- 
five million years to the Grenville strata. Whatever its exact dura- 
tion may have been, the time is utterly inconceivable to us, and the 
important thing to bear in mind is that the great events of earth 
history which have transpired since that time require a lapse of 
many million years as shown by the enormous accumulations of 
sediments in many parts of the earth, and by the building up and 
wearing away of one great mountain range after another. The 
reader will better appreciate the significance of these statements 
after he has studied the following pages. In the table of geological 
time divisions given in chapter 1, the two oldest periods are the 
Archean and Algonkian respectively. The Grenville can not with 
certainty, as yet, be placed in either of these periods, although ac- 
cording to the best evidence it should be classed with the Archean. 
In the meantime it is advisable to refer to all formations older than 
the Paleozoic simply as Precambric. 
LIFE IN THE GRENVILLE OCEAN 
All that can be said regarding the life of the Grenville ocean is 
that it existed as indicated by the presence of the graphite. Al- 
though we can not even state whether the organisms were plant or 
animal, the fact that there was life in that very ancient ocean is a 
matter of no little significance. Anthracite coal, which is chemically 
