Pacific Railroad crosses the divide, forming the source of the Frazier and Saskatchewan rivers. Many mountain streams whose sources are at present in no way connected may have been so at no very remote period. All of our streams which have their sources within the glaciated area were no doubt connected as the ice receded. The drainage of Lake Champlain and the lakes in central New York was southward at the close of the glacial epoch. It is said that in times of high water one may pass in a skiff from the head waters of the Mississippi to the Red River of the North. With such facts before us we can easily understand why the fishes of two rivers whose sources are near each other should be most nearly alike nearest the divide. If the two rivers were formed about the same time, as no doubt were the James and the Ohio, they would naturally have several species in common. In other words, the two fish faunas will resemble each other throughout their whole extent. In the case of the Missouri and the Columbia, the former is much the older stream, and while their sources have fishes common to both streams, in the lower parts of the rivers the fish faunas are entirely different. The upper Missouri river and its tributaries are for the most part inhabited by Rocky Mountain fishes, practically the same fauna as we find in the Columbia, but few species characteristic of the Mississippi valley have been able to even cross the great plains and none have ever passed the Rocky Mountain divide.