Besides the relics of the _Mylodon_ and of Man the cavern has yielded bones and teeth, and many horny hoofs belonging to a kind of extinct horses; and this constitutes one of the puzzling things about this cave treasure. The cave is in a part of the country very difficult to reach, and though Sir Thomas Holdich and Mr. Hesketh Prichard made efforts to reach it again and explore it systematically and scientifically, there is a great deal about it that seems likely to remain unexplained. The bones that were found are not buried in lime or any preserving stone; but lie in sand where one would expect them to have perished long ago if they had been of any great age. Yet side by side with them are the bones of a long-extinct horse; and there is no tradition among the Indians to-day of any huge beast corresponding to the _Mylodon_. Sir E. Ray Lankester has pointed out that the whole of South America has been submerged and has risen (and is rising still) for many centuries. Possibly the rocks and high lands where the _Mylodon_ cavern occurs formed an island during the submergence, where a number of early animals took refuge and survived until the re-elevation of the land--and so lived on in the present condition of the land surface until fifty or a hundred years ago. The great land tortoises (like the Galapagan[17] tortoise) have similarly survived on a few equatorial islands. Possibly, though it does not seem very likely, the _Mylodon_ is still living in similar caverns in this region, as yet unvisited by man. [Footnote 17: Of the Galapagos Islands.] In Australia, the land of the marsupials or mammals with pouches, the bones of many gigantic creatures belonging to that tribe of animal have been found. Giant kangaroos, twice as tall as the biggest living kangaroo, wombats and voles as big as a rhinoceros, have been discovered. One of these is the _Diprotodon_, which Sir Richard Owen reconstructed much in the same way that he reconstructed the _Moa_, and of which Dr. Stirling has since found complete specimens in a morass in South Australia. [Illustration: Diprotodon Equal in size to a large rhinoceros. (Remains found in Australia.)] Last of all of the great extinct mammals which we shall mention is the Mammoth, which has a peculiar interest because, like the _Mylodon_, it certainly survived until man was on the earth, as there are many more evidences to prove.