In the seventeenth and eighteenth centuries it was not an uncommon subject of academic and learned discussion.[375] It was a part of the survey made by many of the writers who discussed the origin of the American tribes, like Garcia,[376] Lafitau,[377] Samuel Mather,[378] Robertson,[379] not to name others. It was not till Humboldt compassed the subject in his _Examen Critique de l’histoire de la géographie du nouveau continent_ (Paris, 1836), that the field was fully scanned with a critical spirit, acceptable to the modern mind. He gives two of the five volumes which comprise the work to this part of his subject, and very little has been added by later research, while his conclusions still remain, on the whole, those of the most careful of succeeding writers. The French original is not equipped with guides to its contents, such as a student needs; but this is partly supplied by the index in the German translation.[380] The impediments which the student encounters in the _Examen Critique_ are a good deal removed in a book which is on the whole the easiest guide to the sources of the subject,—Paul Gaffarel’s _Etude sur les rapports de l’Amérique et de l’ancien continent avant Christophe Colomb_ (Paris, 1869).[381] The literature of the supposed old-world communication with America shows other phases of this question of ancient knowledge, and may be divided, apart from the Greek embraced in the previous survey, into those of the Egyptians, Phœnicians, Tyrians, Carthaginians, and Romans.