You will remember, when we were discussing the general subject of volcanoes, in the beginning of this book, that we spoke of volcanic mountains being bottled up after an eruption, by the hardening of the lava which remained in the crater and the tube that connects the crater with the place from which the lava had been derived. We then spoke of this hardened mass being known as a _volcanic plug_, or stopper, explaining how the volcano could never again erupt through its old crater unless it could develop sufficient force to blow out or remove this stopper. Now besides the crater at the top of Mt. Taylor there were several others in the eroded region surrounding the mesa, or high table-land, from which Mt. Taylor rises. When, therefore, the erosion which removed the 2,000 feet of rocks on all portions of the old mesa that were not protected by the coating of lava, these old mountain plugs were too hard to be worn away or eroded, and were, therefore, left projecting into the air like vast pyramids. If you should ever visit Mt. Taylor and should go to the eastern border of this mesa, and look over the eroded plain, you would see in the lowlands a part of the places from which the 2,000 feet of matter have been slowly eroded. Dutton describes the beautiful panorama that is to be seen as follows: "The edge of the mesa suddenly descends by a succession of ledges and slopes, nearly 2,000 feet into the rugged and highly diversified valley-plain below. The country beneath is a medley of low cliffs and bluffs, showing the browns and pale yellows of the Cretaceous sandstones and shales. Out of this confused patchwork of bright colors rise several objects of remarkable aspect. They are apparently inaccessible eyries of black rock, and at a rough guess, by comparison with the known altitudes of surrounding objects, their heights above the mean level of the adjoining plain may range from 800 to 1,500 feet. The blackness of their shade may be exaggerated by contrast with the brilliant colors of the rocks and soil out of which they rise, but their forms are even more striking." These black piles are the _necks_ or lava plugs of extinct volcanoes. They rise above the level of the plain because, being harder than the surrounding rocks, they have resisted erosion. In some cases these necks or plugs have been converted by shrinkage, on cooling, into beautiful columns, somewhat of the type of the basaltic columns of the Giant's Causeway. It would be difficult to count the number of volcanic necks that can be seen near the edge of the mesa. One's attention is at once attracted to some dozen of these piles, which are especially striking on account of their great size, and ominous black color, but the number is by no means limited to this dozen. There are hundreds of them.