Still another remark is necessary in these preliminary observations. The authorities upon which we have to depend for our knowledge of American antiquities are widely conflicting. There is not one that may be followed unreservedly, and it is impossible to say with any degree of exactness what is even the concensus of opinion of authorities upon very many subjects, so widely divergent and conflicting are their views. This conflict of opinion extends to such important subjects as the following: Who were the first inhabitants of America? Were they indigenous races, or is their presence in America due to migration? If due to migration, from what lands did they come? Was there one or several migrations? What was the course of their migration? Are they of one or a number of distinct races? Are the monuments of civilization found in America ancient or comparatively modern? Do they represent the civilization of vanished races, or are they the work of the not very remote ancestors of the Indians? Is the civilization represented by these monuments really of a very high order, or was it but a step or two removed from savagery? In support of any one of these conflicting opinions about America's ancient inhabitants and their civilization one need not be at a loss to find respectable authorities. One may support with honored names in this field of research the Lost Tribes of Israel theory of the origin of the American Indians; the Malay theory of origin; the Phoenician theory; the Egyptian, the Atlantic, and a number of other minor theories. [19] One can array a formidable list of authors in favor of the indigenous theory of origin for ancient American civilization; and perhaps a still longer and equally learned list of authorities in favor of an exotic origin. All of which makes it evident that writers upon the subject are to be weighed as well as counted; and also warns us that in the presence of such a diversity of opinions many things pertaining to American antiquities must remain open questions. It must be remembered that as yet, so far as man's researches are concerned, but little is really known about ancient America. "That," as a Frenchman remarks, "has yet to be discovered." True, many of her ancient monuments have been located, but they seem to tell a different story to each explorer who looks upon them. There are not wanting stone tablets of hieroglyphics, and ancient documents written on skins and paper; [20] but up to the present time they are sealed books even to the learned. Meantime no Rosetta Stone is discovered [21] to furnish the key to their decipherment, and no learned American Champollion as yet [22] comes forward to reveal their mystery.