The interest which this piece of geologic history has for us in this connection is the presence of man in America during all the time that these tremendous events were taking place. We know he was there, from the evidence he has left behind him in the various strata and deposits attributable to the different agencies I have described. How far back his most ancient relics carry us, is not quite clear. By some, the stone implements from Table Mountain, California, and a skull found in the auriferous gravel in Calaveras county, California, are claimed to antedate any relics east of the mountains. These stone utensils are, however, too perfect, they speak for a too specialized condition of the arts, to be attributable to a primitive condition of man; and as for the Calaveras skull, the record of its discovery is too unsatisfactory. Furthermore, in a volcanic country such as the Pacific coast, phenomena of elevation and subsidence occur with rapidity, and do not offer the same evidence of antiquity as in more stable lands. This is an important point, and applies to a series of archæological discoveries which have been announced from time to time from the Pacific coast. Thus, in Nicaragua, human foot-prints have been found in compact tufa at a depth of twenty-one feet beneath the surface soil, and overlaid by repeated later volcanic deposits. But a careful examination of all their surroundings, especially of the organic remains at a yet greater depth, leads inevitably to the conclusion that these foot-prints cannot be ascribed to any very remote antiquity.[10] The singular changes in the Pacific seaboard are again illustrated along the coast of Ecuador and Peru. For some sixty miles north and south near the mouth of the Esmeraldas river there is a deposit of marine clay six or eight feet thick underlying the surface soil in a continuous stratum. Under this again is a horizon of sand and loam containing rude stone implements, and what is significant, fragments of rough pottery and gold ornaments.[11] This shows conclusively that an extensive and prolonged subsidence took place in that locality not only after man reached there, but after he had developed the important art of the manufacture of clay vessels. This was certainly not at the beginning of his appearance on the scene; and the theory of any vast antiquity for such relics is not tenable. The lowest, that is, the oldest, deposit on the eastern coast in which any relics of human industry are claimed to have been found, is that known as the “Columbian gravel.” This is considered by geologists to have been formed in the height of the first glacial period. From its undisturbed layers have been exhumed stones bearing the marks of rough shaping, so as to serve the purpose of rude primitive weapons.[12]