Wrangell was much struck by the wonderful skill displayed by the sledge drivers in finding their way by the wave-like ridges of snow formed by the wind. These, formed on the level sea ice by any wind of long continuance, are called _sastrugi_ in Siberia. The ridges always indicate the quarter from which the prevailing winds blow. The inhabitants of the _tundras_ often travel over several hundred miles with no other guide than these _sastrugi_. They know by experience at what angle they must cross the greater and lesser waves of snow in order to arrive at their destination, and they never err. It often happens that the true permanent _sastrugi_ have been obliterated by temporary winds, but the traveller is not deceived. His practised eye detects the change, he carefully removes the recently drifted snow, and corrects his course by the lower _sastrugi_, and by the angle formed by the two. On his third journey, Wrangell started northwards from the coast on March 16th, 1822, chiefly with the object of ascertaining the truth of a native rumour that there was high land in that direction. But again, after travelling for many days through ranges of hummocks, showing there must have been heavy ice pressure during the winter, he came to weak unsafe ice at a distance of 170 miles from the land. He was away 55 days and went over 900 miles, a little over 16 miles a day. May 5th saw them back at Nijni Kolymsk. The fourth journey was begun on March 14th, 1823. At Cape Chelagskoi a Tchuktche chief told Wrangell that, on a clear summer’s day, snow-covered mountains might be descried at a great distance to the north, and that herds of reindeer sometimes came across the ice, probably from thence. The natives concurred in stating that Cape Jakan was the nearest point to this northern land. Wrangell struck off to the north when he had gone a little way beyond Cape Chelagskoi. A violent gale came on, and cracked and broke up the ice, placing the party in considerable danger. They only succeeded in crossing the cracks owing to the incredibly swift pace of the dogs. Wrangell was obliged to turn back at a distance of only 70 miles from the land. Even then the men had to ferry themselves across many cracks on pieces of ice, the dogs swimming and towing, the temperature of the sea being +28° Fahr. This was in the end of March. Lanes of water were opening in all directions and, without a boat, the little party was placed in a position of extreme danger. The gale dashed the pieces of ice together with a loud crashing noise, and broke some of the floes into fragments. The dogs alone saved them. Land was reached on the 27th March, and Wrangell continued the coast survey for some time longer, returning to Nijni Kolymsk on May 10th, after an absence of 78 days, having travelled over 1530 miles.