The deposits of the vast region west of the Missisippi had been found to be richer than those of any other region yet explored, in the reamins of vertebrates, or backboned animals.  First the interest had been in finding things unknown before, giving them names and describing them, and it was well, for that was the first work to be done.  Their when it was seen that there were many successive formations containing as many successive faunas and floras the center of interest was in the demonstration of evolution and in constructing family trees of