U-IN-KA-RET MOUNTAINS. 201 
there were valleys along their courses. Other streams had their sources far 
away to the south, and came down into the Colorado, and it is probable 
that they also ran through valleys. Then these displacements began; they 
were not formed suddenly; the rocks were not flung down during some 
great convulsion, but settled slowly, so that this change in the contour of 
the surface had no effect on the course of the streams. Thus the downfall 
of the beds was not faster than the wearing away of the channels, for the 
displacements by faults and folds has not determined nor modified the direc 
tion of the principal streams. As the rocks fell, molten lava was thrust up, 
not suddenly, nor all at once, but from time to time now here, now there 
pouring out a sheet of molten rock in one eruption, and again in another, 
and this commenced away back in that time before the shales and sand 
stones seen in the Vermilion Cliffs had been carried away from the benches 
and plateaus to the south. Doubtless these first floods of lava found their 
ways into valleys valleys in that elder time and covered great beds of 
these sandstones and shales. When the lavas cooled, the rocks which they 
formed were much harder than the sandstones by which they were under 
laid, and the beds which formed the surface of the country elsewhere; and 
as the degradation of this region by rains and rivers continued, the surround 
ing country was carried away, and the sandstones and shales, protected by 
the harder beds of basalt, remained; and now mountains stand in such 
places, doubtless marking the sites of ancient valleys. So the uncovered 
sandstones wasted away, and the lava-capped beds remained, leaving at 
first low tables,, covered with sheets of basalt. Still, from time to time, new 
beds of lava were poured out not over the old beds, usually, but on their 
borders, increasing their protected area; and, as the surrounding sandstones 
were still farther carried away, still, pari passu with erosion, came floods of 
lava, and thus the mountains which remain have a strangely complex con 
stitution. We may call them eruptive mountains, for, had no eruption 
occurred, no mountains would have been left; all of the sandstones would 
have been carried away. But yet the great mass of the material of which 
the mountains are made is not eruptive matter; the mountains are great beds 
of sandstone and shale, covered with blankets of basalt, and, in a general 
way, the older beds of lava have the higher position on the mountains. 
20 COL 
