Page:Popular Science Monthly Volume 7.djvu/552

534 and the foot of Gray Cañon, rocks of Cretaceous and Jurassic Age are found, but they are soft, and have not withstood the action of the water so as to form a cañon.

These formations differ not only in geological age, but also in structure and color. It will be interesting to notice how these structural differences affect the general contour of the country, and modify its scenic aspects.

In the description of the three cañons in the history of their exploration, the attentive reader has already noticed the great variety of geological and topographic features observed as we passed along.

Let us now take a view of the three lines of cliffs. The Brown Cliffs are apparently built of huge blocks of rock, exhibiting plainly the lines of stratification. The beds are usually massive and hard, and break with an angular fracture. The whole is very irregular, and set with crags, towers, and pinnacles. The upper beds of the Book Cliffs are somewhat like those last described, and they form a cap to extensive laminated beds of blue shales, in which we see exhibited the curious effects of rain-sculpture. The whole face of the rock is set with buttresses, and these are carved with a fretwork of raised and rounded lines, that extend up and down the face of the rock, and unite below in large ridges. The little valleys between these ridgelets are the channels of rills that roll down the rocks during the storms, and from one stand-point you may look upon millions of these little water-ways.

Labyrinth Cañon is cut through an homogeneous sandstone. The features of the cañon itself have been described, but the cliffs with which it terminates present characteristics peculiar to themselves. Below, we have rounded buttresses, and mounds and hills of sand, and piles of great, angular blocks; above, the walls are of columnar structure, and sometimes great columns, seen from a distance, appear as if they were elaborately fluted. The brink of this escarpment is a well-defined edge. But if these formations extended over the underlying beds at one time, and if they have been carried away by rains and rivers, why has not the country between been left comparatively level, or embossed with hills separated by valleys? It is easy to see that a river may cut a channel, and leave its banks steep walls of rocks; but that rains, which are evenly distributed over a district, should dig it out in great terraces, is not so easy to perceive.

The climate is exceedingly arid, and the scant vegetation furnishes no protecting covering against the beating storms. But though little rain falls, that which does is employed in erosion to an extent difficult to appreciate by one who has only studied the action of water in degrading the land in a region where grasses, shrubs, and trees, bear the brunt of the storm. A little shower falls, and the water gathers rapidly into streams, and plunges headlong down the steep slopes, bearing with it loads of sand, and for a few minutes, or a few hours, the