40 THE OCEAN RIVER 



winds, the ocean surface continually evaporates, leaving the 

 accumulated salt behind and giving up fresh water to the 

 clouds. When these release their rain upon the land the cycle 

 is completed. The net result would be a continual slow increase 

 in saltness of the ocean, but there is no general agreement 

 among scientists as to the rate of this increase, or even whether 

 it has occurred at all. It has been suggested, however, that 

 at the time when our remote ancestors were beginning to 

 acquire an improved chemical control system, their body 

 fluids became stabilized at the same strength and chemical 

 composition as the ocean in which they lived, and that the 

 ocean was at that remote period only half as salt as it is today. 

 Thus the blood coursing through our bodies today may well 

 be a chemical reminder of the earlier ocean stream which 

 bathed the body surface and permeated the tissues of our far 

 ancestors. 



Life in the Ocean River has not always been the same. 

 Though the oceans have probably existed in their various 

 forms for nearly 2,000 million years, there were no fish of any 

 kind until less than 400 million years ago, and even the smaller 

 shellfish and Crustacea did not come into being until after the 

 earth had reached at least three-quarters of its present age. 



Our knowledge of this ancient sea life is drawn from the 

 sediments deposited in the shallow seas and on the submerged 

 continental plains during those periods when the land was 

 inundated and the course of the River changed so radically. 

 These deposits now form limestones and other rocks thou- 

 sands of feet thick in various parts of continental Europe and 

 North America. Similar sediments were laid down in other 

 parts of the world, when other oceans spread their borders over 

 the continents. But the great bulk of our knowledge of past 

 life in the ocean has come from the fossilized beds of Tethys, 

 the ancestral Mediterranean Sea, from the great gulfs and con- 

 tinental seas of North America, and from other ancient 



