64 Professor G. Forchhammer on the Downs of Denmark. 



much inclined to assume that the strength of storms increases 

 towards the north, that for a long time I could not give credit to 

 my observations. A glance, however, at the map fully explains 

 the phenomenon. With us, the most violent storms come most 

 frequently from the north-west, and it is exactly where the 

 downs begin to diminish that the southern part of Norway pre- 

 sents itself as a protection against this direction of the wind ; 

 and hence it need not surprise us, that plantations of trees 

 succeed in the valleys of the Downs of Skagen, while, on the 

 island Sylt, three degrees farther south, attempts to plant 

 have hitherto failed. 



The material of which the wind has formed the downs is 

 sand, generally beach-sand, which originally seems to have 

 been derived from the great brown-coal formation. In the 

 south this down-sand is mixed with many white plates of mica 

 of the same formation, and this has given rise to the incorrect 

 assertion, that the drift-sand is distinguished from. other sand 

 in this, that it consists of small plates of quartz. In the 

 north, near Skagen, the down-sand contains much titanic- 

 iron and garnet, both of which are likewise derived from the 

 brown-coal formation. The size of the moving grains of sand, 

 which depends on the strength of the wind, is most consider- 

 able where the downs are highest. At List 30 of the largest 

 grains weighed 790 milligrammes, while the same number at 

 Ager weighed only 200 milligrammes.* 



The form of a down in the act of formation is different from 

 that presented by a broken-up down. The former presents a 

 gently inclined flat surface, varying from five degrees to ten 

 degrees towards the direction of the prevailing wind which pro- 

 duces it, that is, towards the west or north-west. It is only 

 where a new down is formed on an old broken-up down that 

 many larger angles occur, whiehj'^however, are only exceptions. 

 In the direction opposite to that of the prevailing wind, a down 

 presents a much higher angle, which, I may say, is constant ; 

 for it amounts everywhere to thirty degrees, where the for- 



* Downs always abound much in water,' owing to their capillary action, 

 and, on their heights, it is seldom necessary to dig more than a foot to meet 

 with wet sand ; in the valleys of the downs fresh water is immediately en- 

 <:ountered on digging. 



