There have also been various discoveries which are said to place the human species in America previous to the appearance of the glaciers. Some remains of man’s industry or of his skeleton have been reported from interglacial, others from tertiary deposits.[27] Unfortunately, these finds have not always been sufficient, or not of a character to convince the archæologist. I have before adverted to the impossibility, for instance, of an archæologist accepting the discovery of a finely-polished stone implement in a tertiary gravel, except as an intrusive deposit. It is a violent anachronism, which is without a parallel in other countries. Even the discovery of a compound implement, as a stemmed arrowhead, in strata of tertiary date, is, with our present knowledge, quite out of the question. Although there are well recognized signs of glacial action in South America, it is not certain that the glacial epoch coincided in time in the two continents. That there was a reasonable approximation is probable from the appearance of later deposits. We may suppose therefore that the habitable area of the New World was notably less at that period, and that the existing tribes were confined to a much narrower space. This would force them into closer relations, and tend powerfully to the production of that uniformity of type to which I have before referred. We might also expect to discover in the tropical regions of America more frequent evidence of the primitive Americans than in either temperate zone. This has not been the case, probably because the geologic deposits of the tropics have been less investigated. Throughout the West Indies there is an entire absence of palæolithic remains. Those islands were first peopled by tribes in the polished stone stage of culture. In the valley of Mexico human remains have been disinterred from a volcanic deposit of supposed tertiary age, and you have all heard of those human footprints which Dr. Earl Flint has unearthed in Nicaragua. These are found under layers of compact volcanic tufas, separated by strata of sand and vegetable loam. There can be no doubt of their human origin or of their great antiquity; but no geologist need be informed of the difficulty of assigning an age to volcanic strata, especially in a tropical country, subject to earthquakes, subsidence and floods.[28] It would not be in accordance with my present purpose to examine the numerous alleged finds of human remains in the strata of the tertiary and quaternary. All such furnish data for the pre-historic chronology of America, and should be carefully scrutinized by him who would obtain further light upon that chronology. I must hasten to some other considerations which touch the remote events to which I am now alluding.