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ting stops for a long distance in an icy acclivity, and its scalp is always snow-clad. The pines and larches disappear at five thousand, nine hundred feet, while the mosses and lichens continue up to the line of perpetual snow. The cerealia are not grown higher than three thousand, eight hundred, or four thousand feet, but in one sheltered place, Skala, barley ripens at five thousand, nine hundred and fifty feet above the sea.

In order to produce glaciers there must be a marked relief and depression of the surface and a marked vicissitude between the summer and winter temperature. While the Andes in the tropics rise into the region of perpetual congelation, there is not that variation of temperature which is necessary to produce neve, that aggregation of large crystalline facets, so different from river-ice, which make up glaciers. Many parts of Siberia and North America are within the line of permanent ground frost, and yet no glaciers are formed. In the Alps, according to Forbes, the summer's thaw percolates the snow to a great depth with water. The frost of the succeeding winter penetrates it far enough to freeze it to at least the thickness of one year's fall; or by being repeated in two or more years, consolidates it more effectually. The glacier commences near the line of perpetual snow, and renewed by the accumulation of each winter descends to a lower level, its extremity being constantly dissolved by the summer's heat.

In the Colorado region the conditions of relief and depression of surface are sufficient to maintain glaciers, but the temperature is not sufficiently low to maintain a line of perpetual congelation on which they depend for their existence.

Glacial Action.—Two enquiries naturally suggest themselves; were these mountains formerly encased in ice? Were these plains subjected to that erosive action so conspicuously displayed in New England and the region of the Great Lakes?

The western limit of the Erratic block group, as observed by me, is in the immediate valley of the Missouri, between Leavenworth and Lawrence. The western limit of the striated rocks, as observed by Hayden, is at Plattsmouth, also in the immediate valley of the Missouri.

In crossing the plains, which expand to more than six hundred m'les in width, there is an absence of all drift phenomena, such as boulders, gravel knolls, and planed surfaces, until Denver is approached. Here the soil reposes on a water-washed gravel, but the beds of the streams are composed of shifting sands. Advancing towards the foothills, small boulders are observed strown over the surface, and occasionally it is traversed by ridges of sand. In fact the observer experiences a feeling of disappointment at the absence of the more striking drift phenomena; for naturally comparing this region with the Alps, he expects to see great outlying masses of rock which have been transported far from the parent bed ; accumulations of gravel and sand in the nature of terminal moraines; and rock surfaces which have been planed down and striated. Entering the mountains, the cliffs are jagged, no where exhibiting those smooth outlines seen in the Alps and called by De Saussurc, roches moutonnees. The enclosing banks of the streams are made up of largo egg-shaped pebbles and occasional boulders two and three feet in diameter. None of these materials, so far as I have observed, are striated, while the true drift pebbles are almost invariably marked by such signs. Taking Clear Creek as the line of my observation, these waterworn materials do not attain an elevation above its bed of more than one hundred feet, and tracing the smaller streams to higher elevations they soon disappear and are replaced by angular fragments.

The transporting power of the present streams is very great. They have a descent of from fifty to one hundred feet to the mile, and, swollen by the spring freshets, the waters sweep down with sufficient force to bear along the largest boulders here observed, particularly if entangled in ice.

Another phenomenon characteristic of all true drift regions, is entirely wanting on the plains, and but sparingly- represented in the mountains; and that is the absence of lakes. Professor Ramsey, as far back as 18G2, in a paper communicated to the Geological Society of London, pointed out the fact that lakes were very numerous in those regions where the evidences of ice action were most manifest, and comparatively rare in tropical and subtropical regions; and maintained that they were actually due to the erosion of their basins by glaciers.

The scenery of the Alps derives one of its principal charms from the abundance of its lakes. "We may refer to Geneva, Constance and Zurich, near the borders of the mountains, to the Lakes of the Four Cantons, Lago Maggiore, and Como, and the series of Austrian lakes, to say nothing of the innumerable pools of water which occur near the summits of the loftier ridges. The scenery of Sweden and Norway is diversified by these inland enclosures of water, which become rare in the more temperate elirnates.

If we consult a map of the northern portion of our own country, we shall find that, leaving out the great chain of the Canadian Lakes, and such collections of water as Winnepeg, Athabasca, Slave Lake and Bear Lake, all the way from Minnesota to the Arctic Sea, there are innumerable smaller lakes which enable the voyageur in his canoe to penetrate to every portion of the country. In southern Wisconsin the lakes are few and in Illinois they disappear almost altogether.

On the plains there is not a permanent collection of water to which we attach the name of lake; and in the mountains they are rare. This is the more surprising when we consider how actively the forces of elevation and subsidence have been exerted. The Great Basin, it is true, is characterized by numerous lakes, most of which are of a highly saline or brackish character, but in a region where the streams are cut off from the sea, it is but natural that the waters .should accumulate in the depressions.

There may have been a time when the annual precipitation of rain was greater, and consequently the transporting power of the streams was increased beyond their present capacity, but there are few phenomena with regard to the distribution of the superficial materials which cannot be explained by a resort to causes now in operation. Professor Whitney has arrived at substantially the same results with regard to the Pacific slope.

In concluding these observations, I may remark that the railroad facilities are now so far developed that to an inhabitant of the Mississippi Valley, this region is as accessible as the White Mountains of New England. The ordinary observer is brought in contact with some of the grandest scenes in nature, whilst to the geologist and botanist are opened new spheres of observation — a constantly recurring succession of the most interesting and varied phenomena.

IRRIGATION AND THE FLORA OF THE PLAINS.

BY E. L. GREENE.

The system of irrigation is destined to effect some interesting changes in the aspect of the western plains in regard to their botany, as will appear from a few facts which we subjoin as the result of observations made in Colorado during the past two seasons.

It might be expected that refreshing streams conducted through this naturally rich, but extremely arid soil, would have flowerybanks. So indeed it does sometimes happen, and so it would always be if the diggers of ditches would make them broad and shallow, with gradually sloping banks, instead of digging them narrow and deep and leaving the sides perpendicular.

God speed the labors of the " grim utilitarian;" for when he has plowed, and scattered the "precious seed," we know that with the wheat, there will spring up and bloom the purple corn cockle, and the yellow evening primrose — one joy for him and three for us. Or, if his skill divides the mountain stream, causing a portion of its waters to turn from their natural course adown the valley, and leads them over the thirsty plains that lie above, the happier are we ; for while now from the face of the " desert" he reaps golden harvests, we see it "rejoice and blossom as the rose."

We will suppose that the reader is a botanist, and that he has come out from the far Atlantic shore, to pass a few summer weeks among the mountains. Arrived in Denver, the next point to be gained is Golden City, the gateway to the mountains. He might traverse this short distance in less than a half hour by rail, but of this mode of conveyance, excellent as it is, some three thousand miles, more or less, he is now doubtless tired; besides, he wishes to see something of the vegetation of the plains before, leaving them for the rocks and the pine-forests, the alpine bogs, and the fields of perpetual snow. You then take this little trip to Golden City on foot. It is July or August. There has been no rain for these many weeks. The road is miserably dusty, but if you are on foot (or on horseback) you need not follow it, and the whole surface of the plains is sere and brown save some "eighties"or larger tracts that are fenced, and under cultivation.

You have perhaps crossed a broad, deep canal of swiftly-flowing, muddy water, and now in passing these fields of grain you hear the laughing voices of little streams. They are hidden from view by the standing growth, and at proper distances from each other they go, singing on their way across the gently sloping fields, making glad the hearts of the ranchmen, with their sure promises of an abundant harvest. Now right in the midst of one of these "eighties" of wheat, you behold a solid-half-acre of—can it be? Yes, those are certainly the long strap-shaped leaves, and the dark cylindrical spikes of Typha latifolia! the veritable Cat-tail Flag; and growing more densely and luxuriantly than you ever saw it before.

It is difficult to harmonize, in your mind, this patch of marsh with its close surrounding of thrifty grain, and equally difficult is it to reconcile the whole field with what seems to shut it in on all sides i. e. a seeming boundless, lifeless waste of withered prairie grass. There are now, on these plains, many acres of Cat-tail Flag where live years ago, no seed of a marsh plant would have germinated, because all was then more like an African desert than an American swamp. The change came after the following manner. The large ditch was first made from some stream before it leaves the mountains, and led along the higher ground, whence its waters were conducted to these lands below, which now constitute fertile fields. After one or two seasons of irrigation, all slight hollows came to be occupied by shallow ponds. Why the surplus waters do not sink away into the earth beneath, you must learn from the geologist. The fact is they do not. Even during fall and winter when the water is turned off from the ditches, the ponds remain the same, the water in them falling but slightly below the ordinary level.

The gossamer-winged seeds of the Typha are borne upon the winds by the thousand, from the valleys of the rivers below, to these uplands. Here they find all circumstances favorable to germination, and the plants grow and spread rapidly; sedges and other marsh plants growing with them, and the whole comes in the course of a few years to bear a strong contrast to the almost desert tracts around.

In the settled, and consequently irrigated, portions of country

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