is gradually digging into the plateau occupied by Shavers Fork, a tributary of Cheat River. Leatherbark Run is an ambitious stream, with a fall of more than a thousand feet in less than a mile and a half, and is now only four hundred yards from one of the tributaries of Shavers Fork. It will not be long, geologically speaking, before it captures its prey, and a falls dropping into a picturesque gorge should mark the scene of the Leatherbark's victory. THE ANDROSCOGGIN ATTACKS THE CONNECTICUT The falls at Berlin and Gorham, New Hampshire, are memorials of the time when the Androscoggin River broke through the preglacial divide near the Maine-New Hampshire line, at the foot of Mount Winthrop, and, capturing the drainage of northeastern New Hampshire from the Connecticut River, delivered it into the Kennebec at Bath. When the Androscoggin cut through the divide in order to despoil the Connecticut's preserves, it made an easy route for a railroad, which now shares the pass with the river. Utah affords another interesting case of this type of lawlessness. The Provo River originally rose on the western slope of the Wasatch Range. Beyond these mountains was the south fork of the Weber, another enterprising stream that formerly had its headwaters on the west slope of the Wasatch, but later succeeded in cutting through and extending its territory into the western end of the Uinta Mountains. Finally the Provo broke through also, and, attacking the high floor of Rhodes Valley, pushed on until it tapped the south fork of the Weber, thus despoiling that stream of half its water and increas ing its own strength correspondingly. This capture was so recent that the entrenching of the stolen stream is still going on. THE ADVENT OF PASSIVE PIRATES In the foregoing instances of stream stealing, the rivers and creeks that made the captures were aggressive and daring Brethren of the Main. There are other streams, however, that have played a more canny rôle. They have craftily laid low and waited until unsuspecting Nature should drive the quarry into their grasp. One of the most effective aids of these passive privateers was the great ice sheet that thousands of years ago swept down over the northern part of the United States. It covered Long Island, northern New Jersey, the northeast and northwest corners of Pennsylvania, and then swept on westward through Ohio, Indiana, Illinois, Iowa, and the Dakotas to the Rockies. Prior to its advance the rivers within its limits were different in aspect, direction, and location from what they are today. Many of them were entirely obliterated or forced into new beds; others had their direction of flow reversed and were obliged to pay tribute to stronger streams. The great Ice Age was indeed a dramatic period in American geological history. Rivers that had flowed north were forced to abandon their outlets and seek others southward; animals that lived in the north were driven southward, and the whole area was transformed by the onsweeping hand of destiny. WHEN THE ICE SHEET BEGAN TO RETREAT The highest point on Mount Desert Island was covered by the flood of ice. Mount Washington probably had only the tip of its summit above the surface of the glacier, which also passed over the Green Mountains where they are upward of 3,000 feet high. Mount Tom, Mount Monadnock, Mount Holyoke, and the Berkshire Hills all slept beneath its icy sheet. The Catskills were barely able to hold their heads above its onrush, and it left its mark on the summit of Elk Mountain, in Susquehanna County, Pennsylvania. With our knowledge of the great ice. gorges that frequently occur to-day in such rivers as the Susquehanna, the Delaware, the St. Lawrence, and the Missouri, we may well imagine what this mountainous invader from the north did as it advanced, and what floods it crested when the returning warmth melted it away. The Mohawk River is a classic example of how pirate streams gained rich prizes without aggression at this stage of earth affairs. Before the ice invasion, the ancient Mohawk rose at the head of a di WHERE ONE GOES UP TO THE MISSISSIPPI In its lower reaches the Mississippi has become so feeble that it can no longer carry off all the sand and silt its tributaries and upper stretches bring to it. Hence it is gradually filling up its own bed, and but for man-built levees would spread its sluggish self over millions of acres of land. How long engineers can go on building up its banks as it fills up its bed is a question often asked, but not yet successfully answered. vide at Little Falls and flowed westward as a confluent of the preglacial St. Lawrence. At the same time a tributary of the Hudson had worked its way up to the east side of the Little Falls divide. Bed rock to-day slopes westward and eastward from that point (see map, page 92). In its course southward the ice blanket dammed up the St. Lawrence and the Mohawk alike, and the waters were all driven south through the Mississippi, the Ohio, the Susquehanna, and kindred streams. Then the ice began to melt, the front gradually retreating northward. Finally, the valley of the Mohawk was uncovered, and it received tremendous floods of glacial water which ultimately drowned the river and converted its valley into a lake. Higher and higher the deluge rose, finally finding the weak spot in the shoreline at Little Falls. PREPARING FOR A 60-FOOT DIVE: TURNER FALLS, OKLAHOMA Headwaters of streams often cut through mountains themselves to prey upon other rivers. At other times they capture parts of the water of other streams without invading the streams themselves. For instance, the high peaks of the Teton Mountains of northwestern Wyoming all lie east of the water parting, or actual divide. The rivers flowing east have a more rapid descent than those flowing west, and therefore are gradually forcing the actual divide westward. Given sufficient time, they will be able to eat their way through the Rockies, even as the tributaries of the Tennessee force their way through the Great Smokies (see text, page 99). Rushing through this saddle in the divide, it fell into the tributary of the Hudson, a gift from the gods. With this vast new accretion of power, the Hudson's affluent began to tear away the vitals of the divide in deadly earnest, and before the ice front had retreated far enough north to uncover the St. Lawrence, had entirely destroyed the barrier between it and the ancient Mohawk and had hoisted its flag permanently over the territory of the latter stream. Meanwhile the Susquehanna, attracted by the rich spoils the Mohawk Valley offered, had pushed its headwaters within eyeshot of the ridge on the south side of the Little Falls gorge. But the Hudson carried the day and has held the prize throughout the intervening ages. The battlefield at Little Falls, where the capture was made, is a striking place for such a tragedy. The high and rugged ridges that mark the valley gradually close in as one travels eastward from Herkimer, until they come so close together at Little Falls that there is room enough Majestic cathedrals and temples have been carved by the hurrying river, threading its way through the great Kaibab Plateau. only for the river, the Erie Canal, and the New York Central lines. Shortly after passing that point they separate again and the valley grows wider. THE OHIO A CANNY CORSAIR The Ohio captured and has held streams driven into its grasp by the advancing ice. Before the coming of the Ice Age that river had its headwaters near New Martinsville, West Virginia. In those days all of the present drainage of that stream north of New Martinsville flowed into Lake Erie. The Monongahela joined that part of the Allegheny south of Thompsons Gap with its confluents, as now, at Pittsburgh, and, avoiding the present elbow in the Ohio at Beaver, flowed past Youngstown into Lake Erie near Conneaut, Ohio, through a now extinct river variously called by geologists the Grand, the Spencer, and the Pittsburgh. The advance of the ice sheet dammed back these waters, which, looking for a point of escape, reversed a little tributary whose headwaters were opposite those of FLOWING ROCK IN SILVER BASIN, COLORADO The high cliff, attacked by the air, slowly crumbles, and the great deposits of talus acquire slopes too steep for stability, and a stream of rock begins to wend its glacierlike way toward the stream that drains the area. the Ohio at New Martinsville. At the latter point they overflowed the divide and joined the Ohio. As in the case of the tributary of the Hudson, once the Ohio had succeeded in getting momentary control of the magnificent host of waters the ice had driven into its lair, it worked with terrific energy to hold them. Its campaign was successful, for when the ice floods were stayed it held the gorge at Beaver and was able to swing the waters of all the captured streams around the elbow at that point and lead them southward past New Martinsville. It also held possession of all the terri tory up to the present-day divide that lies hauntingly close to Lake Erie. Indeed, near Dunkirk, New York, one may stand at the parting of the waters between Lake Erie and the Gulf of Mexico and look down into the lake itself. That part of the Allegheny River above Thompsons Gap was once a northwardflowing stream, with its headwaters on the north slope of the divide at that point. The ice sheet that aided the Ohio had perhaps somewhat earlier aided the lower Allegheny by damming back the northbound waters and forcing them across the divide into the very lap of the Allegheny. That river accepted the prize and led it |