166 THE OCEAN RIVER 



air and sea produce a more uniform and less revolutionary 

 climate. Before that can happen we can expect with some 

 certainty a renewal of the icecaps. But our own immediate 

 climatic environment has become temporarily settled so re- 

 cently that we need not worry about perihelions or the imme- 

 diate creation of mountain ranges or the break-through into 

 the Pacific. Nonetheless things are afoot that do affect us. 

 Let's begin with the last retreat of ice only 15,000 years ago, 

 and see what our climate has done since then. 



It is obvious that as the icecap over northern Europe began 

 to draw back the living conditions favorable to mankind's 

 survival also increased — at first, probably, round the sea 

 fringe of the European continent where forests began to 

 grow. This story is told in the annual layers of sediment called 

 'Varves" laid down by the Baltic and other bodies of water 

 which were then inland lakes near the retreating edge of the 

 ice. By the year 12,000 b.c. the Baltic was well established as 

 a huge fresh-water lake closed off from the warm currents of 

 the Atlantic Ocean. The accelerated melting of the icecap 

 after this time raised the level of the ocean. Between 8,000 

 and 7,000 b.c, at the time of the earliest Near Eastern civiliza- 

 tions, the Atlantic waters burst through into the Baltic. After 

 another thousand years the land bridge between lake and 

 ocean closed again, and did not reopen until some time be- 

 tween 5,000 and 4,000 b.c. In this Littorina period the waters 

 of the North Atlantic were warmer than today, and heavy 

 forests covered the seacoasts of northern Europe. 



The climate from 4,000 b.c. on became warm and moist, 

 dominated by the influence of the Atlantic currents pene- 

 trating into the Baltic. At this time the glaciers disappeared 

 from the Alps, and the northern icecap had little influence 

 on the climate. From 3,000 b.c. on for about ten centuries 

 in this Atlantic period, mild and equable conditions reigned 

 over Europe. Egypt and the kingdoms of the Near East were 



