Near Buck creek itself the ant-hills contained only small sharks' teeth, showing that they were still built over marine beds. Then as one mounted the divide and with it crossed higher and higher strata there was a long interval of totally unproductive formicaries, until the principal bed of lignite was reached, and above this, at a vertical distance of ten to fifteen feet, the best of the ant-hills were found, which contained among other remains the bones, scales and teeth of fresh-water fishes allied to the gar-pikes living to-day in southern rivers. These were carefully preserved for comparison with the mammal-bearing sands at Yale collected by the older expeditions, and which were found later to include, in addition to the mammals, fossils exactly similar to those which we secured at this time. That we had found an old locality was further proved by indications of a former camp, fire wood, rusted tin cans, and in an adjacent ant-hill tiny, worn fragments of an unfortunate investigator's spectacles!
The mammalian relics which were thus found were of very small size, consisting of individual teeth or a fragment of a jaw with one or more teeth still in position, or other portions of the bones. Mammal teeth are fortunately highly indicative of habit and relationships; but on the other hand, in collections of this sort, not one bone can be associated with another. Thus, while some idea of the general size and method of feeding may be obtained, no attempt to restore the skeleton or even the entire skull is possible. In size none of the ant-hill mammals was larger than a rat, and many were much smaller. Those whose teeth bore few sharp-pointed cusps were carnivorous, feeding on such feeble folk—insects, worms, and possibly other mammals—as they could overcome. Others with chisel-shaped incisors and many-cusped grinding teeth were plant-feeders, probably living not only on tender leaves, but on berries and the seeds of berries and other fruits.
The little glimpse of a former geologic age which this trip gave us was full of suggestive detail. I have already described the scene as the scientific imagination conjures it up, the broad, savanna-like, low-lying lands over which wandered the huge reptiles then at the very culmination of their evolution. But what of the mammals? Where were they and how did they survive the competition with the dinosaurs? Possibly their very insignificance was their chief safeguard, just as countless small rodents and insect-eating creatures live to-day in the lion-and buffalo-haunted African jungles. Possibly they were tree-inhabitants, and the location of the mammal-bearing ant-hills near the lignite certainly suggests an abundance of near-by vegetation. However we may interpret it, the evidence is clear that these mammals and the dinosaurs were contemporaries in the same general locality though the exact environmental conditions under which they lived may have differed.
Passing back in time some millions of years further, one finds in
