[Footnote 3: Formations Sedimentaires, p. 498, Anal. Mus. Nac. Buenos Aires, ser. 3, t. 8.] [Footnote 4: Neues Jarhbuch fur Mineralogie. bd. 21, p. 193.] [Footnote 5: Princeton Expeditions Reports, vol. 4, p. 303.] Without going into the history of the various positions which different authors have taken, and which will be found given in detail in Wilckens’ paper, or in less detail in Ortmann’s, we will consider the positions of the most recent students of the question. Ameghino postulates a marine and a continental series of deposits being laid down more or less simultaneously. In the marine series below the Deseado, which is grouped as Guarantic, he places the Luisa, the Roca and the Salamanca, followed by a hiatus, then the Sehuen, which in turn is followed by another hiatus and the end of the Cretaceous is reached. The Patagonian is his Eocene. Parallel to the marine series is the terrestrial, where the Casamayor (= Notostylops) is contemporaneous with the Salamanca, the Deseado with the Sehuen, and the Colpodon, the Notohippus and Astrapothericulus with the Patagonian, thus making the Deseado of Cretaceous age. After a very detailed study of a large series of Patagonian fossils, Ortmann concludes that the Patagonian is of Lower Miocene age. This is the most detailed study which has been made. Wilckens coincides with this view, though feeling that the Patagonian may have extended down a trifle into the last of the Oligocene. This latter author finds a long gap between the Upper Cretaceous and the Patagonian, a period when Patagonia was above water. It was during this interval that the Casamayor, the Deseado and possibly other beds were deposited on the continent. I have gone over Ortmann’s argument, and studied a large collection of Patagonian fossils, both vertebrate and invertebrate, of my own; and while there are some places where we would like further data, I can come to no other conclusion but that these Patagonian beds are Lower Miocene, the exact relationship with beds in North America and Europe, being as yet not definitely settled, nor will this be possible until a study of the migrations of the elements of the Patagonian fauna has been made.