further results would have followed from the existence over the country of this continental ice sheet, he will see that the rocks and soil carried away by the glacier must have been again deposited when the movement ceased and the ice and snow of which it was composed had melted away. This means then the laying down of this vast amount of rocks and soil over the region which had been planed, and it is this sort of covering which makes up the greater part of the soil over that portion of the United States shown in the accompanying map. If one compares the overlying soil in this region with that in the Southern States, for instance, he will find great differences, for the soil there, except where ancient river or ocean beds occur, has originated in place avoidance of this area by the glacier: one that the bed of Lake Superior lying north swallowed up so much of the ice that there was little to be passed onward and the other that the dryness of the region caused the amount of ice and snow which it received to be small. Considering now again the deposition of the rock and soil by the melting of the glacier it will be seen that two agencies would effect its distribution-the first gravity, the second water. The melting of the glacier would be marked by streams of water in every direction, which would float and distribute such of the material as they could carry, but the large boulders would evidently remain very nearly where they lay when the onward movement of the glacier WIDENING OF VALLEY WALLS BY DOWNWARD CUTTING OF STREAM. by the decomposition of the rocks imme- ceased. We should expect, therefore, heaps of large boulders and pebbles in some places, and in others broad, flat accumulations of fine soil, especially of a clayey nature, since this is usually found in glaciers formed of the fine particles by the wear of the rocks on each other. Of course, in any single hill or plain, numerous variations from fine to coarse material will probably be found showing variations in the force of the water which prevailed during its formation, but one may expect a general distribution such as I have indicated. It would be expected that this deposit while taking place all along the glacier's path as it melted back would be especially large in quantity at the terminus of the glacier, and this is found to be the case. For this reason the region along the terminus of a glacier will have a topography peculiar to itself and one which may soon be recognized when the eye becomes accustomed to it. It is known as "morainic" topography, from the term "moraine" given to the accumulation of debris borne by a glacier, and may be described as a billowy, hummocky, tumultuous landscape such as would be produced if a collection of gravel heaps made by children at play were magnified each to hills varying in size from a hundred to a thousand feet in diameter. There are many such morainic areas to be seen over the States the swift rushing waters are dropped as soon as the slope and speed diminish and how in quiet pools or where the flow is sluggish, even the fine silt can be held no longer and is laid down. He should note how at any particular point deposition varying from coarse to fine resulting from changing speeds of the current produces a succession of layers, which, known as strata and preserved when the whole is consolidated into rock, would show the nature of their origin. He should note how the cutting power of the stream is exerted rearwards as well as laterally, and that the backward movement tends to subdivide constantly into new branches so as to give the valleys an amphitheater like shape and keep the slope constantly steep. He should note with what unerring touch the stream distinguishes the hard strata or veins from the soft and cuts away the latter while leaving the former standing in relief. He should note how in its lower course where the slope is less steep, the stream is choked by the deposition of material which it can no longer carry, the valley is broadened and the stream winds in it from side to side. He should note how with a diminution in the of the Middle West. One at Lemont, Illinois, is shown on page 1668. It is evident that the flowing waters from the glacier and the subsequent continuous drainage of a region will have another effect besides that of mere deposition. They will carve and shape the deposits already made. Since such carving by running water has been one of the most effective agents in forming the striking features of a landscape, one should study it thoroughly. One should observe a running brook or even the rills from a recent rainfall and see what a constant carrier running water is, always moving rock and soil nearer the sea. He should note how the size of the particles carried varies with the speed of the water, how the large pebbles borne by THE PEBBLES OF A BROOK BED ARE SORTED ACCORDING TO THE RATE OF FLOW OF THE WATER. (Photo by H. Wm. Menke.) amount of water or increase of speed in this portion the stream may cut a gorge in the broad plain it had previously formed and leave the former plain terraced above its waters. These are but a few of the observations which may be made upon almost any running stream and which will be seen to typify and interpret the behavior of all streams and rivers. Considering again the effect of the continental ice sheet and its deposits it may be seen that previous systems of drainage must have been profoundly modified by the filling in of former river and lake beds and that new systems of drainage must have been started in many cases. Records of former drainage systems may be observed by keeping a lookout for old river gorges and lake beaches such as are common over a glaciated region. While the ice was melting moreover, dams were formed producing temporary lakes, some of which were of great size. One called Lake Agassiz occupied a large part of what is now Minnesota and Manitoba and was 700 miles in length. The conformation and outlets of what are now the Great Lakes were many times changed and the tracing of these changed outlines is a work of much interest. In order to be able to recognize the existence of former lakes, one should study the modern ones, noting their topographic features and the manner in which they are produced. Like streams, lakes both erode and deposit, but in ways peculiar to themselves. The prevailing winds produce currents which erode material in one place to deposit it in another. Between headlands. the waters usually are quiet and a curving beach is built such as by its perfect symmetry of form delights the eye. The headlands too are continually being worn away by the cutting edge of the waters, which sawing under the cliff or bank tend to keep it perpendicular by the fall of the overlying material. Currents from two directions meeting in the lake likewise produce an area of still water where the silt they were carrying will be deposited and a bar or spit be formed. These may or may not rise above the surface of the waters so as to be visible while the water covers the area, but if the water is withdrawn by recession of the lake their existence becomes evident. The present site of Chicago exhibits numbers of these ancient reefs as well as beach lines marking former higher levels of Lake Michigan. Turning from the mantle of drift to consideration of the solid rock beneath, one finds that it calls for only a further application of the principles which have just been considered. A large proportion of the rocks of the earth's crust are made up of layers or strata showing deposition by water and hence called stratified rocks. An area of sandstone differs from a bed of sand simply in being more firmly consolidated either by cementing waters or the pressure of overlying layers. lying layers. The bank of drift represented in the cut previously noted would, if consolidated into rock, form what is known as a conglomerate or pudding stone. Most limestones represent deposits formed by marine life, such as mollusks, corals, etc. Of such deposits forming at the present day the best illustrations are to be seen along coral reefs or in coral islands. Such conditions must have been nearly reproduced in former times to have formed the great limestone beds characterizing the central United States. Rocks not appearing stratified may be (1) stratified rocks, the layers of which have been obliterated by heat and pressure. Such are called metamorphic rocks and include gneiss, marble, slate, etc. (2) They may be igneous rocks such as are poured out by volcanoes or forced up in dikes from the heated earth's interior. These include granite, basalt, obsidian, etc. The occurrence of such rocks in place is evidence of previous igneous action and often a whole series of volcanic phenomena may be traced in a region which now gives no apparent evidence of such activity. One such region is to be found, for instance, in central Wisconsin. It is in the stratified rocks that such economic deposits as those of coal, oil, gypsum, and in some cases lead and zinc occur, while most metalliferous deposits of value are confined to veins in the igneous rocks. The latter are the source of most ores of gold, silver, copper, mercury, tin, nickel and, to a large extent, of lead. In seeking to follow out any given formation whether of economic value or not, one must consider the possible dislocations it may have suffered. For instance, it is evident from the nature of their origin, that stratified rocks must have been originally deposited in a nearly horizontal position. Yet we find them often tilted at a high angle, as illustrated in the accompanying cut, or even sometimes completely |