Edinburgh Geological Society. 065 
formation (the ‘‘ Loess’’) which Lyell calls ‘‘inundation mud,” and which. 
he designates as the last and latest of all the great formations known to 
geology. The difficulty of accounting for it is proved by the number 
of theories which have been propounded. The shells in that formation 
are not fluviatile, nor are they lacustrine. On the other hand, they 
are not marine. They are terrestrial. They are land shells—the 
shells of damp woods or morasses—in short, of a land surface which 
has been covered with this ‘‘inundation mud.’’ One possible expla- 
nation is obvious. The sea establishes its own forms of life where 
itself is established for any length of time. But if its invasion of any 
land area be not lasting, but temporary, it may well fail to carry its 
mere dead shells over that area, whilst its living fauna would not 
have had time to grow. But here, again, at all costs, this notion of 
a submergence temporary and transitory must at all hazards be dis- 
missed. And so the ice-cap again comes into play. There are no 
banks within which to confine a great European lake, but in the ice- 
sheet banks are always ready; and so it has been supposed, among 
other explanations, that enormous masses of ice, walking of their own 
sweet will about the world, came down from the north and dammed 
back the waters of the Rhine, or of some other greater river which 
then took its place, and thus formed a lake in which this vast sheet 
of inundation mud was deposited. I do not pretend to be able to 
solve all the difficulties of the problem connected with the great 
formation of the ‘‘ Loess.” But I am sure that any theory is better 
than this; and, further, I am sure that many difficulties will be 
removed if we can but face the conclusion that there has been in very 
recent times, and over a large area of the northern hemisphere, a great 
depression and a great re-emergence of the land towards the close of the 
glacial epoch. 
I pass now to another fact and problem connected with Pleistocene 
Geology, which is of the highest interest and importance. I refer to 
the bone caves of the south of EKurope—caves not like almost all those 
found in this country, into which bones more or less numerous have 
been brought by men or by hyenas, but caves packed from floor to 
ceiling with a breccia mainly consisting of the skeletons of the great 
Pleistocene Mammalia, of the Rhinoceros, the Hippopotamus, the 
Mammoth, the Lion, and the large associated Graminivora. Chiefly 
in the countries bordering on the Mediterranean such caves have been 
found in abundance, containing such a mass of animal remains that it 
is certain that no agency but that of water could have brought them 
aud huddled them up together in such heaps at one spot. For many 
years it has appeared to me that no existing theory accounted satis- 
factorily for such an assemblage of such creatures under such con- 
ditions. Lyell’s explanation seems to me very unsatisfactory. In the 
Morea, and in other limestone countries, it is said some rivers lose 
themselves in swallow-holes, and run the rest of their course—or. 
long distances of their course—through channels under ground. It 
is assumed that the great pachyderms, during a long course of 
ages, were perpetually tumbling into such rivers, and were being 
carried, each separately and singly, into the subterranean channels, 
until at last in particular places those channels become choked. 
