66 Professor G. Forchhammer 07i the Downs of Denmark. 



relations arise, which can only be explained by the internal 

 structure of downs. Each down is stratified, and, in such a 

 manner, that it has one plane of stratification corresponding 

 to the inclination towards the wind, therefore, generally 

 speaking, an angle of five degrees towards the west ; and a 

 second, which inclines under an angle of thirty degrees, to the 

 east. This stratification is exhibited in the alternation of fine 

 and coarse grains, whose deposition is produced by the differ- 

 ent degrees of strength of the wind. As the downs increase 

 chiefly on the inner side, this is the prevailing direction, which, 

 however, undergoes numerous modifications. When a gentle 

 wind blows, it matters not from what direction, the down is 

 furrowed, and presents a gently waved surface. This circum- 

 stance is extremely well marked in the northern portion of 

 Jiitland, where the down-sand contains titanic iron. There, 

 each small wave-like eminence, hardly an inch high, is formed 

 of white quartz sand, while the depression consists of black 

 titanic sand, and, by means of this distinction of colours, the form 

 of the surface is very distinctly brought out. The wind-furrows 

 on the surface of the downs are just as perfect as the water-fur- 

 rows of the horizontal sandy surfaces which are from time to 

 time flooded by the sea ; and, notwithstanding the greatest 

 attention, I have never been able to detect the slightest dis- 

 tinction between the two. This is easily explained, because 

 these water-furrows are produced by the direct action of a 

 gentle wind on the water, at the place where it bows, when 

 the water thus transfers the waves of air only to the sand. 

 It results, therefore, that the stratification is not always a sign 

 of a covering by water, for here we have strata formed one 

 hundred feet above the level of the sea. But other features 

 likewise present themselves here, which are remarkable, and 

 occur not unfrequently in older formations. Thus, when a 

 wind, which is somewhat stronger than that which forms the 

 furrows, sets the down-sand in motion, the coarser sand re- 

 mains lying behind ; and, therefore, when the direction of 

 the wind is diff^erent from the prevailing one, it will form a 

 surface which cuts the plane of stratification. If now the pre- 

 vailing direction of the wind be reversed, the formation 

 of downs is continued as it formerly proceeded, and there is 



