ANT-HILL FOSSILS 241 



mingled. It seemed as though the outer crust and the coarse char- 

 acter 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 wel- 

 comed 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 at- 

 tacked 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. 



VOL. LXXXVII. 17. 



