PICKETT'S SILURIAN CAVE. 



PICKETT'S SILURIAN CAVE. 



BY H. C. HOVEY. 



Every one who visits Colorado is surprised at certain features of scenery to 

 be accounted for only by considering the peculiar geological structure of the re- 

 gion. 



The vast plains, sweeping from the Missouri Valley westward to the foot-hills 

 of the Rocky Mountains, have a gradual upward slope from an altitude of only 

 770 feet above the sea, at Kansas City, to an elevation of 6,000 feet, at Colorado 

 Springs. The underlying rocks, resting on one another, in broad sheets, are 

 varieties of sandstone, limestone, slate and shale, mostly belonging to the creta- 

 ceous formation. 



A glance at the geological map of Colorado shows that large areas of the 

 mountain region are marked as " eruptive," which means that, at some period later 

 than the formation of the plains, there was a great upheaval of the earth's crust, 

 causing the lower rocks to appear at the surface, sometimes by volcanic violence, 

 and at others by the slower process of denudation. These rocks are granite, 

 gneiss, trap, and other hard species, capable of resisting the ordinary action of 

 the elements. 



Along the border line, between the plains and the mountains, is a compara- 

 tively narrow but highly interesting region, lying nearly north and south, where 

 the rocks of the plains, instead of being flat, are turned upward and broken off 

 by the same force that lifted the mountains themselves. It is the opinion of the 

 geologists that these sedimentary beds once extended much further up the mountain 

 side than now, being gradually worn down by the retreating waters of the prime- 

 val ocean, and the subsequent erosion by running streams. 



One of my summer vacations, not long ago, was spent amid the mazes of 

 this border land, and I found it a geological paradise, where the explorer may, by 

 guiding his course intelligently, cross the edges of all the strata, from the Arch^an 

 rocks to the Tertiary, studying the entire history of their folding and erosion, to 

 better advantage, perhaps, than anywhere else on the continent. 



The Monument Group of red sandstones has been repeatedly described by 

 pen and pencil. The fanciful columns of loosely cemented sandstone, each capped 

 by a layer of tough ironstone, that are, in Monument Park, only 10 or 20 feet 

 high, rise to lofty castellated forms in the Garden of the Gods and Glen Eyrie, 

 some of the needle-like spires shooting 300 feet above the green meadows at their 

 base. These grotesque pillars are produced not only by the flowing water, but 

 by the cutting action of whirling sand blown about them by the dry winds of 

 summer. 



Frequently, instead of standing in isolated masses, the red sandstone runs in 

 ribs parallel to the chain of adjacent hills. These ridges are cut through at inter- 

 vals by arches, gateways, caves and tunnels, with very picturesque effect. 



The width of this border region varies from one to twelve miles. Nearest 



