Mr. Downing on the Drainage of Haarlem Lake. 451 



quire the authority of Elib de Beaumont to give force to the supposition of 

 some great subsidence of the land having taljen place, its original conditions 

 being such as to facilitate the formation of a vast extent of peat of considerable 

 depth. 



The range of the rise and fall of tides (a most important physical feature 

 in the artificial drainage of this country, as we shall perceive) is about six feet 

 along the coast of the German Ocean. Within the Zuyder Zee the rise at 

 Amsterdam and in the River Y is barely 2 feet. The prevailing wind is (and 

 we shall find hereafter that this is one most important agent in freeing this part 

 of Holland of its injurious excess of water) the south-west. Nor must those 

 peculiar circumstances of the great intersecting rivers of the Continent, which 

 bear upon the safety of Holland, be omitted here ; these rivers are always fro- 

 zen over in winter, and frequently the rain-fall and melting snows of the higher 

 districts of the Continent are brought down in great volume before the ice in 

 the lower part has disappeared. If, coincident with this, a westerly wind has 

 forced back a spring tide into the mouths of the rivers, and keeping up the 

 shattered ice as a great dam, thus causing the land flood (already, it may be, 

 up to the very edge of the dykes) to rise yet higher, and burst with fury over 

 the now defenceless fields. It is from some conjunction of unfavourable circum- 

 stances, such as those mentioned, that Holland has generally suffered. In 1799 

 the very existence of the country was threatened from this source, the Ehine 

 rising 7 feet in one hour at Nymegen. The improvements in the bed of the 

 river Rhine, even as high up as Bingen, have been a cause of increased anxiety 

 and expense to Holland, by bringing down the waters of land floods and melt- 

 ing snows of the Alps more suddenly upon their dykes. An average of thirteen 

 centuries would show that they have had some severe disaster, either from sea 

 or river, once every seven years. 



The annual amount of rain-fall and evaporation is another natural feature of 

 even greater importance to this than perhaps any other country. The mean 

 fall, deduced from observations of 100 years, is 25-1 in. ; the mean evaporation 

 22'6 in., giving a difference of only 2"5 in. of excess of rain-fall. 



From the earliest times this country has been divided into different dis- 

 tricts, of greater or less extent according to circumstances, which districts are 

 protected and bounded by great dykes that oppose the entrance of the surround- 



