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The Pampean formation, judging from its similar composition, and from the apparent absolute specific identity of some of its mammiferous remains, and from the generic resemblance of others, belongs over its vast area throughout Banda Oriental, Entre Rios, and the wide extent of the Pampas as far south as the Colorado, to the same geological epoch.
Without any communication with the other scientists who were occupied by the same questions, knowing nothing of the results which these experimenters had attained in the case of small mammiferous animals, and which prove that dwarfness has often no other cause than physiological poverty, he confirmed and expanded their ideas from an entomological point of view.
As this latter tooth approaches closely to that of the common horse, I paid particular attention to its true embedment, for I did not at that time know that there was a similar tooth hidden in the matrix with the other mammiferous remains from Punta Alta.
The number of the mammiferous remains embedded in the Pampas is, as I have remarked, wonderful: it should be borne in mind that they have almost exclusively been found in the cliffs and steep banks of rivers, and that, until lately, they excited no attention amongst the inhabitants: I am firmly convinced that a deep trench could not be cut in any line across the Pampas, without intersecting the remains of some quadruped.
The mammiferous animals characteristic of this formation, many of which differ as much from the present inhabitants of South America, as do the eocene mammals of Europe from the present ones of that quarter of the globe, certainly co-existed at B. Blanca with twenty species of mollusca, one balanus, and two corals, all now living in the adjoining sea: this is likewise the case in Patagonia with the Macrauchenia, which co-existed with eight shells, still the commonest kinds on that coast.
We have further seen that in this district, at a period not only subsequent to the deposition of the tertiary strata, but to their upheavement and most extensive denudation, true Pampean mud with its usual characters and including mammiferous remains, was deposited round and between the hills or islets formed of these tertiary strata, and over the whole eastern and low primary districts of Banda Oriental.
But the remarkable fossils for which the Stonesfield slate is most celebrated are those referred to the mammiferous class. The student should be reminded that in all the rocks described in the preceding chapters as older than the Eocene, no bones of any land-quadruped, or of any cetacean, had been discovered until the Spalacotherium of the Purbeck beds came to light in 1854.
The several species of that gigantic genus of birds, the Deinornis seem here to have replaced mammiferous quadrupeds, in the same manner as the reptiles still do at the Galapagos archipelago. It is said that the common Norway rat, in the short space of two years, annihilated in this northern end of the island, the New Zealand species.
They may be said to stand perfectly insulated; they exhibit all the characters of a creation entirely distinct, and except as to the general characters of mammiferous quadrupeds, perfectly of their own kind.
The historian of Columbus does not appear to have been at all conversant in zoology. What the Saavina was cannot be conjectured from his slight notices, unless a basking shark. The other, no way allied to fish except by living in the water, is a real mammiferous quadruped, the Trichechus Manati of naturalists, or the sea cow. The author or his original translator, falls into a great error here.
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