Vol. 57.] CLIMATE OF THE PLEISTOCENE EPOCH. 409 



me that it is after, rather than during, easterly gales, that shells are 

 especially cast up by the sea. 



The sea is agitated during storms to a greater or less depth, 

 according to their violence, and the size of the waves caused by them. 

 Mollusca are at such times rooted up from their usual habitat, and 

 moved forward along the bottom in the direction towards which 

 the wind is blowing. They do not reach the shore during the 

 storm, but after it has ceased. The effect of a strong wind blowing 

 on-shore is to heap up the water against it, and to cause the removal 

 of beach by the undertow of the retreating waves, rather than its 

 accumulation. The material so removed is not carried out far, 

 however, but returns when the wind drops, bringing the dead shells 

 that have become mixed with it during the gale. I learned a short 

 time ago from Mr. A. Patterson, of Yarmouth, that on December 12th 

 or 13th, 1899, the beach at that place, where usually no shells 

 occur, was in places covered with them. On referring to the Daily 

 Weather Charts of the English Meteorological OflBce, I found that 

 the direction and the velocity of the wind, for several days before, 

 had there been as follows : — 



Direction. 

 Force .... 



Dec. 7th. 



8th. 



9tb. 



10th. 



11th. 



12di. 



E.S.E. 



E.S.E. 



E.S.E. 



w.s.w. 



E. 



w. 



8 • 



8 



6 



2 



5 



2 



When the storm abated, the shells were thrown upon the beach. 

 A day or two afterwards, they had quite disappeared, having been 

 covered with sand. 



Meteorology may explain, I think, why dead shells were so 

 constantly cast up on the shores of East Anglia during the Crag 

 Period. The centres of the cyclonic disturbances which approach 

 the British Isles from the Atlantic, pass for the most part, especially 

 during the winter months, to the north or north-west of that portion 

 of the German Ocean which intervenes between Suffolk and Holland. 

 Hence westerly gales (from south-west to north-west) there prevail, 

 and rough seas are common, not only on the Dutch coasts, but on 

 those of France and Great Britain that face the west, and on the 

 eastern coast of Scotland. A typical example of this is given in fig. 2, 

 p. 410, reproduced from the daily weather-chart for January 21st, 

 1899. 



When the regions to the north of Great Britain are anticyclonic, 

 however, which is not often the case during the winter, though this 

 occurred, for instance, on October 17th, 1898 (fig. 3, p. 411), 

 cyclonic storms take a more southerly course, causing easterly and 

 south-easterly gales and rough weather in the East of England.^ 

 Similar conditions may have prevailed, I think, in later Pliocene 

 times. 



As has been long known, the moUuscan fauna of the North Sea 

 was characteristically southern during the earlier stages of the 



^ The weather-charts for the days mentioned above are of a character 

 similar to those reproduced in figs. 2 & 3. 



