Professor G. Forchhammer on the Downs of Denmark, 65 



mation of the down is quite free. It is only where very small 

 flat surfaces occur that this angle reaches forty degrees, and 

 such cases are merely exceptions. In order to explain this 

 constancy in the internal angle of downs, we must have re- 

 course to the mode in which downs are actually formed, and 

 this is, that they increase on their inner side. The sand ascends 

 the gently inclined slanting surface. When it reaches the 

 highest point, it falls, and, as it is there entirely protected from 

 the wind, there is only one condition which exercises an influ- 

 ence on the angle under which the sand is deposited, and that is 

 the size and form of the grains. On the side directed towards 

 the wind, the angle is not only determined by the adherence 

 of the grains of sand with one another, but the wind also 

 strives to spread the grains. As, therefore, the form and size 

 of the grains vary but little upon the whole, inasmuch as they 

 are all polished by the sea, it may be understood how there 

 cauvbe little if any variation in the inner angle of inclination 

 of the downs. The outer side, which is turned towards the 

 wind, is dependent on the strength of the wind, on the acci- 

 dental protection afforded on the coasts, and the like, — circum- 

 stances which vary everywhere ; and hence the diff^erence of 

 angle on that side. It is remarkable that the planting of downs 

 has upon the whole but little influence on their inclination ; 

 it is, in fact, invariably the falling sand which determines it. 



In an undestroyed down, there are therefore no higher 

 angles than those mentioned ; but when, on the other hand, 

 a down is destroyed, other relations occur, which diff^er ac- 

 cording as it has been destroyed by the sea or wind. The 

 demolished downs occur most distinctly where the sea en- 

 croaches on the coast ; and this is more particularly the case 

 on the island Sylt, where not only the wind is strongest, but 

 where for several centuries the current has been pressing on 

 against the coast. Now, when the waves, during high tides, 

 reach the foot of the downs, they undermine the sand, and the 

 downs are cut down perpendicularly, and can remain in that 

 state for a long period, because the sand is kept together by 

 a net of roots belonging to the plants growing on it ; aud 

 hence we always find the sharpest forms of downs directed 

 towards the sea. When the wind destroys a down, peculiar 



TOL. XXXI. NO. LXI. — JULY 1841. E 



