But what broke off these big blocks, these land icebergs that made the basins for the kettle lakes? They were left by the glacier when it began to retreat; that is to say when the supply of snow back at the gathering ground became insufficient to keep pushing it forward as fast as the front melted away. Melting most rapidly in those huge cracks called crevasses, big blocks were finally separated entirely from the main body and left behind as the rest of the glacier slowly melted back toward the mountains. If the glaciers were thus responsible for most of the lakes of the lowlands you may be sure they had a hand in making the lakes of the mountains, right where they themselves live. John Muir, who spent his life in loving study of the mountains of the West and of everything connected with them, found mountain lakes in every stage of existence up the mountainsides; empty stone bowls that showed by the work of the waves on the rocks that they had once held lakes; above these, in the same chain, lakes growing shallow; and, still higher, brand new lakes in stone bowls with the edge of the glacier that had carved out the bowl and filled it with blue water, still bordering it on the upper side. [Illustration: ONE OF THE KETTLE LAKES OF WISCONSIN] And this is why, like fruit on a tree, the youngest lakes are found at the top. Since the glacier melted from the foot of the range upward the lower lakes were the first to be born and the first to pass away; while the lakes higher up on the mountain were the last to be born and the last to pass away. II. The Moods of the Lakes Lakes are like the rivers and the sea; they have their moods. In sunshine and storm, in wind and calm, and from season to season they show many changes. As we already know they are great sleepy heads. To Ruskin mountain lakes seemed both to sleep and to dream. But their longest sleep, like that of Br'er Bear, is taken in the winter. Of this long sleep Mr. Muir says:[37] "The highest (mountain lakes) are set in bleak, rough bowls, scantily fringed with brown and yellow sedges. Winter storms blow snow through the canyon in blinding drifts, and avalanches shoot from the heights. Then are these sparkling tarns filled and buried, leaving not a hint of their existence. In June and July they begin to blink and thaw out like sleepy eyes, the daisies bloom in turn and the most profoundly buried of them all is at length warmed and summered as if winter were only a dream." [Footnote 37: "The Mountains of California."] EVEN THE DUCKS OVERLOOK THESE LITTLE LAKES