INEQUALITIES OF SEDIMENTATION 353 



sea in Holland since the thirteenth century. One of the most 

 remarkable of these changes produced the Zuyder Zee. In the 

 thirteenth century 



the low lands along the Vlie, often threatened, at last sank in the waves. The 

 German Ocean roUed in upon the inland lake of Flevo. The stormy Zuyder 

 Zee began its existence by engulfing thousands of Frisian villages, with aU 

 their population and by spreading a chasm between kindred peoples.^ 



The political as well as the geographical continuity of the land was 

 obliterated by this tremendous deluge. Another of these great 

 inundations occurred in 1570. 



A continued and violent gale from the northwest had long been sweeping 

 the Atlantic waters into the North Sea, and had now piled them upon the 

 fragile coasts of the provinces. The dykes, tasked beyond their strength, 

 burst in every direction. The cities of Flanders to a considerable distance 

 inland were suddenly invaded by the waters of the ocean.^ 



ORGANIC AND BIOCHEMICAL DEPOSITS 



Limestone of biochemical origin. — In the case of non-clastic 

 sediments variability in the rate of accmnulation in different 

 areas is probably as pronounced as it is in clastic sediments. 

 There is little available data concerning the rate at which limestone 

 sediments accumulate. But it is probable that a seasonal factor 

 may become recognizable. The formation of limestones of bio- 

 chemical origin is confined to rather definite geographical areas. 

 Although sea water generally contains about 2,000,000 tons of 

 calcium to the cubic mile^ it is being extracted and built into rock 

 formations within the confines of the tropics and subtropics in far 

 greater quantities than elsewhere. The development of coral 

 reefs, the formation of calcareous deposits by denitrifying bacteria 

 and the lithification of shore deposits are the principal elements 

 in the inequality of the distribution of calcareous sediments. The 

 limitation of the action of each of these agencies to wide belts on 



' J. L. Motley, The Rise of the Dutch Republic, Historical Introduction VI, 

 Vol. I, p. 35 (London, 1913). 



= Op. cit., Vol. II, Part III, chap, v, pp. 285-87. 



3 John Murray, Nature, XXXIX (1889), 426. 



