The Past 3 



times may probably be increased tenfold at least, and the biol- 

 ogist, who formerly complained of lack of time, now has more 

 than he can account for, and has to marvel at the permanence of 

 living types from epoch to epoch, often with very little change. It 

 is also certain that the geological column, as at present known, lacks 

 many horizons, and these, with fossils new to science, may at any 

 time reward the explorer. Standing near the rest house on Flag- 

 staff Hill, at Boulder, and looking northward, we see two parallel 

 ridges, running north and south. The higher and more western, 

 known as Red Rocks, was laid down in Paleozoic times. The vege- 

 tation in those days, though highly developed and diverse, was of a 

 relatively primitive type. The dominant insects were cockroaches, 

 many of them of large size. Fishes abounded in the waters, while 

 tailed amphibians, walking over the wet mud or sand, sometimes 

 left impressions of their feet, which may be seen to this day in the 

 rock. An animal known only by such tracks, very like those of 

 the modern Ambystoma or Tiger Salamander, has been named 

 Limnopus coloradensis by Professor Henderson.* The specimen 

 described was found at Lyons. The more eastern ridge, begin- 

 ning just back of the sanitarium, belongs to the lower part of the 

 Cretaceous period, and is many millions of years later than the 

 Red Rocks. In the interval between the two, mammals, birds 

 and the higher flowering plants have come into existence. The 

 mammals were small, the birds were toothed, but the plants 

 included trees of modern aspect, similar to or not distinguishable 

 by their remains from poplars, oaks, figs, laurels, hollies, beeches, 

 etc. Thus the life of the earth had undergone a radical trans- 

 formation, one carrying the promise of the modern world. Today 

 one can pass from one ridge to the other in a few moments, and it 

 is hard to imagine the great lapse of time represented by the 

 interval. Where are the rocks which should represent that time? 

 In part perhaps never deposited in this vicinity, because deposition 

 in one place means erosion in another, and it is only in certain 

 places, usually along coasts, that materials are laid down to form 

 new strata. In part also, we may feel sure, deposited but subse- 

 quently eroded away, the very thick cretaceous beds being formed 

 out of the disintegrated materials. This erosion is going on today, 



♦Gilmore (1926) records footprint* referred to the same species (which he calls Laoporus 

 color adoens is) from supposed Permian rocks in the Grand Canyon of the Colorado, Arizona. 



