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GLACIATED MOUNTAIN PEAKS, TUOLUMNE VALLEY, CALIFORNIA.

any one time their full significance. We now know, however, that the shapes of the pebbles and the scratches upon them indicate glacial action, and that where we stand amid a landscape clothed in the verdure of summer, but a short time ago, geologically speaking, winter, centuries if not millenniums long, reigned and wrought. So just as the pearly shell held to the ear repeats the story of its ocean home, these faceted pebbles could tell us if we listened of the march of a vast sheet of ice by which they were caught up and swept onward, and in which they were held and rubbed, now against their fellows and now against the rocky floor beneath, until they acquired the shape which they now possess. We know this because we know that it is just what glaciers do to the rocks they carry nowadays, and no other force can quite imitate their effects. Having thus once become aware of the former existence of a glacier in the place where we are standing, the interpretation of every feature around us will be influenced by that fact. If along the roadside we find a place where the blanket of soil has been recently removed so as to expose the hard ledge beneath, the surface of the latter will be seen to be smoothed and leveled, and in occasional exposures, scratches or grooves somewhat like those on the pebbles just spoken of except that they are deeper, more regular and nearly all run in one direction, may be seen. These clearly mark the planing down by the glacier of the surface of the rock over which it passed and the direction of movement. The recording, according to the direction of the compass, of these striæ in several places in any given locality is always a work worthy to be performed, since it gives not only the general direction of

movement of the glacier, but its local variations. Sometimes two sets of striæ can be seen running in different directions, one of them crossing and hence later than the other. These usually mark the movement of a later glacier, for we know that the ice which covered the country advanced and retreated no less than five times. The evidence of these successive stages can be sought to better advantage, however, in the topography of a region than in the markings on the rock surfaces. It is evident that the effect of the movement of such a vast mass of ice and rock over a region must have been to plane down its prominences and smooth and round over the whole area. This smoothing and rounding effect is well shown in the mountain prominences seen in the accompanying cut. Here the glaciation has been so recent that vegetation and decay have not come in and obscured the surface as is the case over most of the area of the

northeastern United States. Contrast this with the high bluffs along the Mississippi river in Wisconsin, which are in a non

glaciated area, or with pinnacles such as Western States, the result of long erosion there are many of in Colorado and other untouched by glacial action and the effect of glacial movement can readily be seen.

If now one thinks for a moment what

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avoidance of this area by the glacier: one that the bed of Lake Superior lying north swallowed so much of the ice that there was little to be passed onward and the other that the dryness of the region caused the act of ve and snow which it received to be sta

Consolering now again the deposition of the rock and so by the melting of the glaDer be seen that two agencies would efect its scrbie-the is gravity, the econd win. The melting of the glacier will be marked by streams of water in very car, whe wood float and dismice such of the material as they could cambo the large boulders would evibently remain very nearly where they lay The the art movement of the glacier

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ceased. The should expect, therefore, beans of large boulcers and pebbles in some rinces and others broad, fu accumulatives of fine soil, especially if a clayey nature, scs is usualy found in cacers formed of the fine patices the wear of the 708 I ad ther. Of CER. I single bill or TALIT THETICS Tariations Sine course material v roadi- be frend show70s the force of vice with prevailed as formacion bet one Tepet i general EstriS SIC as I have indi I would be expected Sturms best the dig 1 10 the glacier's me has wel be

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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 vary-
ing from coarse to fine resulting from chang-
ing speeds of the current produces a succes-
sion of layers, which, known as strata and
preserved when the whole is consolidated
into rock, would show the nature of their or-
igin. 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 amphi-
theater like shape and keep the slope con-
stantly 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 deposi-
tion 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

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EACH ROUNDED

BACKWARD CUTTING BY STREAM.
POOL MARKS LOCATION OF A PREVIOUS FALL.
WATKIN'S GLEN, NEW YORK.

of the Middle West. One at Lemont, Illi-
nois, 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 ef-
fect 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
He should note how the size of the
particles carried varies with the speed of
the water, how the large pebbles borne by

sea.

THE PEBBLES OF A BROOK BED ARE SORTED AC-
CORDING TO THE RATE OF FLOW OF THE WATER.
(Photo by H. Wm. Menke.)

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