When the canals freeze at the approach of winter, they invariably have been observed to disappear in company with the lakes or oases at their crossings. They are then all covered by the reddish-yellow dust carried by wind from the surroundings. When a canal is about to reappear it frequently first comes to sight as a dark streak evidently the result of moistened ferro-oxide. Occasionally a mist formation precedes the appearance of the canal. It is plain that the cold, misty air settles in the valleys, there as here, and gives up its moisture to the salts on their bottom and the canal is thus brought out as a dark line. Sometimes the vicinity also assumes a darker shade indicating the absorption of some moisture. On the sides of the canals the less hygroscopic salts are deposited. Possibly the green colour of the canals is partly a contrast-effect due to the red surrounding, possibly also the result of finely divided matter in the liquid. It is also conceivable that the cause is the reducing influence on the ferro-oxide of the sulphuric gases emerging from the fissures; an exceedingly small quantity accomplishes in this case large results. F. le Coultre describes the colour as being sometimes a dead black. Something similar applies to the seas. When these freeze, especially in shallow places, yellowish-red dust from the continent settles on their surface and lends it hues between the original dark green and the light yellowish-red. When the ice subsequently melts this dust sinks in the water which latter resumes its dark green colour.