OVERSEAS MIGRATION 



algae and other micro-organisms so abundant there. Seasonal abundance of 

 certain forms containing reddish or brown pigments may cause the 'red 

 water' known from ancient time in many parts of the world, and so common 

 is this condition in some enclosed seas that they owe their names to it — the 

 Red Sea and the Vermilion Sea are examples. The colors of the sea are only 

 the indirect signs of the presence or absence of conditions needed to support 

 the surface life; other zones, invisible to the eye, are the ones that largely 

 determine where marine creatures may live. For the sea is by no means a 

 uniform solution of water; parts of it are more salty than others, and parts 

 are warmer or colder . . . And whenever two currents meet, especially if 

 they differ sharply in temperature or salinity, there are zones of great tur- 

 bulence and unrest, with water sinking or rising up from the depth and with 

 shifting eddies and foam lines on the surface. At such places the richness 

 and abundance of marine life reveals itself most strikingly." 



Brooks (1934) says that when one's ship comes "within a few degrees of 

 the equator the scattered cumulus clouds become thicker and grayer, a con- 

 fused swell makes up, rain squalls come and go, and birds appear. At first 

 there is only a greater abundance of storm petrels, with here and there 

 petrels of other kinds hunting along utterly indifferent to the ship, or small 

 groups of tropic birds flying along with the ship, off to one side or overhead. 

 Then scattered groups of various petrels appear, and finally for an hour or 

 two there are birds on every hand. If one is not too far from land, a few 

 hundred miles perhaps, as in the case of the south equatorial drift north of 

 the Marquesas, one may also see multitudes of sooty or crested terns. Occa- 

 sionally one sees the grayish blue form of a shark gliding along, or a big 

 purplish-brown hammerhead lazily twisting around as though trying to get 

 a better view of the ship. Flying fish, while not so closely localized as the 

 birds, are breaking the water every few seconds, and bewitch the beholder 

 by their myriad sizes, shapes and antics, and their bewildering patterns and 

 shades of deep brown, opal blue, yellow and purple. Then the sun comes 

 out again, the sea takes on its deep tropical blue, the birds become more 

 and more scarce and gradually, as the ship moves on, the ocean resumes 

 its desert aspect ... In the North Atlantic ship lanes the same play is 

 staged with different actors. Instead of the equatorial currents there are the 

 Gulf Stream and its continuation, the North Atlantic Drift, and the Arctic 

 Current; instead of confused swells and squalls of rain there are slicks and 

 fogs. Tropic-birds are replaced by jaegers and skuas; and different species 

 of the petrel group, usually here spoken of as shearwaters and fulmars, are 



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