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 bad 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 



