158 
EXTINCT MONSTERS. 
entombed remains of multitudes of animals for ever extinct, and 
reflected upon the time when the country teemed with life, I 
truly felt that I was standing on the wreck of a former world.” 
These old lake-basins, in which so many forms of life have 
been sealed up, all lie between the Rocky Mountains on the 
east, and the Wasatch Range on the west, or along the high 
central plateau of the continent. As the mountains were slowly 
elevated, part of the old sea of the Cretaceous period (that sea 
in which the “sea-serpents” played so important a part) was 
enclosed and cut off from the ocean. Rivers began to pour 
their waters into it, so that the waters became less and less salt, 
until at last a fresh-water lake, or series of lakes, was formed. 
As the upward movement of this region continued these lakes 
were all the while receiving sedimentary materials, such as sand 
and mud, from the rivers, until finally they were filled up, but 
not until the sediments had formed a mass of strata over a mile 
in thickness. Thus we see how favourable were the conditions 
for a faithful record of Eocene life-history. 
But another process was going on which helped to bring them 
to an end ; for they were being slowly drained by the rivers that 
flowed out of them, and these rivers kept on continually deepen- 
ing their channels, so that we have dry land where the lakes 
once were. Now the region is over 6000 feet above the sea, and 
probably more than one-half of these fresh-water deposits have 
been washed away, mainly through the Colorado River. What 
is left of the Eocene strata forms the “ Bad Lands.” The same 
geological action that has cut up and carved out this region into 
buttes, canons, cliffs, peaks, and columns of fantastic shapes, has 
also brought to light the extinct animals preserved in the rocks, 
much in the same way as an old burial-ground, if cut up by 
intersecting trenches, might be made to yield up the bones of 
those who for generations had been buried therein. 
Professor Marsh first discovered remains of Dinocerata in 
1870, while investigating this Eocene lake-basin, which had 
