mingled. It seemed as though the outer crust and the coarse character of the sand on the exposed surface were merely the result of wind and rain which eroded away the finer particles and compacted the surface, and the evidence of the coarser grains on the westward side simply pointed to the removal of somewhat heavier material here than elsewhere by the prevailing westerly winds. I imagine that these winds were also the determining factor in the placing of the entrance, although the idea that the warmth-loving insects might thus have welcomed the rays of the rising sun did occur to me.
It has been found that in addition to ordinary sand-grains certain of the ant-hills also contain fossils, tiny teeth, bone fragments, and in rare instances perfect bones which the ants had unconsciously collected and which have been the source of much of our knowledge of the smaller forms which were contemporaneous with the giant reptiles. It was toward these ant-hills, therefore, that our attention was turned, indeed, they were the object of our journey. I had a rather imperfect map of the region which was supposed to show the place where each important dinosaur specimen had been found and to indicate in a general way the mammal-producing areas. With its aid a very thorough exploration was made, the great majority of the localities which were marked being searched for ant-hills, and these in turn for fossils.
The older method was to shovel the contents of the formicaries into sacs and leave them until the following day, when the ants would have left the material, and then to sift it very carefully, searching for the minute remains of organic life. Much of the "pay dirt" was shipped directly to New Haven, where it could be investigated more thoroughly than was possible in the field. Our time, however, was very limited, so that such refinement of method was impracticable. Then, too, we were not so intent upon adding to the already great collection at Yale as upon determining the exact stratigraphic sequence of the mammal-bearing beds with reference to the geologic column. We therefore attacked the ants' stronghold at once, going over the surface material very carefully, taking the precaution, however, to put a little earth into the entrance and pat it down, thus reducing to a minimum the number of available defenders. The sand was then passed through a common flour sifter and the residue carefully examined, the tiny teeth and bones being removed with a pair of forceps. We did not come away unscathed, for though we brushed aside all the ants we saw, the task would become so absorbing that before one knew it an ant would fix her jaws into the skin and, turning the abdomen under, insert the short but thoroughly efficient sting. After sifting the material we generally replaced it about as it had been found and, as the ants were uninjured, their fabric was probably soon restored to its former symmetry by the tireless little workers, for whom we had a very respectful sympathy in spite of our wounds.