606 THE UNIVERSE. 



ble darkness towards the bottom. The ancient Hercynian 

 Forest, which we had just traversed, was buried under half 

 a yard of rime ; the cold was 25 below freezing-point 

 (Fahr.) ; and our vehicle, in spite of the skids, which made 

 large showers of ice fly on all sides, dragged us with fright- 

 ful rapidity towards the precipice. It was altogether su- 

 perb, and vividly recalled the icy forests of the north. 



Sometimes, on the contrary, the mountain tops, in splin- 

 tering off, have left upright, here and there, long, narrow 

 segments of rock, which, seen from afar in the dim mists 

 of night, seem like so many fantastic shades hovering in 

 the clouds. These are the witch-dances of the superstitious 

 inhabitants of the Harz forests. 



When the rending asunder of mountains takes place on a 

 grand scale, and their flanks are deeply cut into, advantage 

 is taken of the natural openings thus formed in order to 

 trace out roads or passes, distinguished by the name of 

 gates, because they offer easy means of communication be- 

 tween nations. The Iron Gates of Algeria have acquired a 

 certain degree of celebrity. 



It should also be remarked that certain gorges are due to 

 the erosion of thq waters alone, which, rolling over their 

 walls, incessantly wear them away, and in time form large 

 valleys. These gorges of erosion are less rugged than 

 those caused by rents ; the waters, by the friction of the 

 fragments carried down by them, and by their own move- 

 ment, having smoothed their sides. Often, also, rivers roar 

 at the bottom of these ravines, leaping over the pebbles, or 

 precipitating themselves from fall to fall amid the rocks. 



Many of the cascades which we meet with among moun- 



