the clear water and allow the sediment in the bottom to dry. If the water in the glass was six inches deep, there will finally remain in the bottom a mass of hardened mud, which will vary in amount with the time of the year in which the experiment is performed, but will average about one-fiftieth of an inch in thickness. Each cubic foot of the water, then, must contain nearly six cubic inches of solid sediment or silt.

It has been estimated that the average flow of the Colorado River at Yuma throughout the year is eighteen thousand cubic feet of water per second. From this fact we can calculate that there would be deposited at the mouth of the river every year, enough sediment to lie one foot deep over sixty-six square miles of territory. Nearly one three-hundredth part of the Colorado River water is silt, while in the case of the Mississippi the silt forms only one part in twenty-nine hundred.

FIG. 3.—LOOKING TOWARD THE DELTA OF THE COLORADO FROM YUMA

Now we are prepared to understand the origin of the vast lowlands about the head of the Gulf of California. Long ago this gulf extended one hundred and fifty miles farther north than it does at present, so that it reached nearly to the place where the little town of Indio now stands in the northern end of the Colorado desert.

When the Colorado River first began to flow, it emptied its waters into the gulf not far from the spot where Yuma is situated. The water was probably loaded with silt then as it is now. Part of this sediment was dropped at the mouth of the stream, while part was spread by the currents over the bottom of the adjoining portions of the gulf. The rapidly growing delta crept southward and westward into the gulf. As fast as the sediment was built up above the reach of the tide, vegetation appeared, which, retarding the flow of the water at times of flood, aided the deposition of silt and the building up of the delta.

As the centuries went by, these lowland plains became more and more extensive, until the gulf was actually divided into two parts by the spreading of the delta across to the western shore. The portion of the gulf thus cut off from the ocean formed a salt lake fully one hundred miles in length.

We may suppose that for a long time before the barrier was high and strong, the tidal currents occasionally broke over the delta and supplied the lake with water. As the river meandered here and there over the flat delta, its channels must have undergone many changes at every time of flood. A part of the water without doubt flowed into the salt lake, and another portion into the open gulf. In fact, the basin in which the lake lay, now known as the Colorado desert, continued to receive water from the river, at intervals, until very recently. In 1891 an overflow occurred, through the channel known as New River, which flooded the lower portion of the basin and threatened to cover the railroad.

When the ocean had been permanently shut off from the head of the gulf, and the river itself had been largely diverted toward the south, the lake began to dry up. At last, most of the water disappeared and there remained a vast desert basin, at its greatest depth two hundred and fifty feet below the level of the ocean. In the bottom of the basin a bed of salt appeared, for this substance could not be carried away, as the water had been, by the thirsty air.

Remarkably perfect beaches still exist around the shores of this old lake, and on them are found the pearly shells of multitudes of fresh-water mollusks. The presence of these shells leads us to believe that after the salt lake dried up, the river again broke in and formed a new lake of comparatively fresh water which also, after a time, dried up.

The wonderful fertility of the Colorado delta is just beginning to be appreciated. Canals have been dug to take the water from the river and distribute it over the land. Year by year the cultivated lands are being extended. The change which irrigation is making upon the surface of one of the worst deserts in the country is indeed remarkable.

The Colorado River is working on quietly and steadily. We may think, and truly, that it has already done a great at work in excavating the mighty cañons along its course, but, in reality, the work already accomplished is small in comparison with that which remains to be done.

In time, if the land is not disturbed by the forces which build mountains, the plateaus through which the river now flows in such deep cañons will be carried away in the form of sand and mud. Broad valleys will replace the cañons, and the Gulf of California will become a fertile plain. As the highlands wear away the process will go on more and more slowly, for there will be less rainfall. The river will become smaller and its basin more arid. All these changes will be brought about through the crumbling of the rocks, and the removal of the waste matter by the running water.

A TRIP INTO THE GRAND CAÑON OF THE COLORADO

We may read of the Colorado plateau, and of the Grand Cañon with its precipitous walls of variously colored rock, but unless we actually visit this wonderland, it is hard to realize the height and extent of the plateau and the depth of the gashes made in its surface by running water, gashes so deep that they seem to expose the very heart of the earth.

Nature has chosen a remote and half-desert region for the location of this, the most picturesque cañon in the world, as if she wished to keep it as long as possible from the eyes of men. Once a traveller could not view the cañon without making a long and weary journey across hundreds of miles of desert; now it is quite different, for one can almost look into its depths from the windows of a palace car. But to appreciate and understand fully the stupendous work that nature has done throughout this region we must leave the cars at a somewhat distant point, and before reaching the cañon become acquainted with the country in which it lies through the old-fashioned ways of travelling on horseback or wagon.

Flagstaff was formerly the starting-point for travellers to the cañon, and we will choose it now, for the old stage road offers an interesting ride. The road first winds around that lofty snow-clad peak, the San Francisco Mountain, which can be seen from all northern Arizona. Leaving the mountain behind, we strike out directly across the high plateau. The country is nearly level, and the open park-like forest extends in every direction as far as one can see.

It is difficult for us to believe that we are seven thousand feet above the sea, a height greater than that of the highest mountains in the United States east of the Mississippi Valley. It is this elevation, however, which brings the summer showers and makes the air cool and pleasant, for the lowlands of this portion of the United States are barren deserts, upon which the sun beats with almost savage heat.

After the rainy season green grass and an abundance of flowers appear in the open meadows scattered through the forest. But, as a rule, the entire absence of water strikes one as being very strange. Where are the springs and running streams which usually abound in mountainous regions? Throughout the whole distance of seventy miles from Flagstaff to the cañon, there are but one or two spots where water is to be found. These places are known as "water-holes"; they are simply hollows in the surface of the ground where the water collects after the showers.

There is another strange feature about the plateau over which the road leads; instead of sloping down toward the Colorado River and the Grand Cañon,