190 GEOGNOSY AND GEOLOGY. 
dropped into the subjacent or associated caverns, or accumulated in the 
narrow galleries of the roof or sides. The richest deposits are frequently 
found in horizontal or inclined galleries or excavations in the roof of the 
cave, and under such circumstances as to preclude the possibility of ar 
introduction through the mouth or main entrance. Such sink-holes may 
also seem to explain the introduction of certain foreign earth-beds and 
masses into the cave, as also In some measure the excavation of the cave 
itself. 
Some of the most celebrated bone caves are the Baumann’s-cave and 
Biels-cave in the Hartz, the cavern of Gailenreuth (pl. 52, fig. 9, in section), 
and the Wirksworth cave in England (pl. 38, fig. 68, in vertical section). 
Among other remains, the complete skeleton of a rhinoceros was found in 
this cave. Its skull and horn are shown in pl. 40, figs. 14 and 15. Similar 
caves are found in other parts of England and Germany, in France, 
Russia, and in other portions of Europe. Of other parts of the world, 
Brazil is extraordinarily rich in such caverns. Dr. Lund has investigated 
nearly 200 of these, and obtained a large number of extinct species. Few 
bone caves have hitherto been found in North America, although in the 
abundance of caverns it is exceedingly probable that many are ossiferous. 
Remains have been found in the Mammoth cave of Kentucky, in a cave 
of Greenbrier county, Virginia, and in several caves of Cumberland county, 
Pennsylvania. 
It will thus be seen, that our division of the tertiary after Hausmann and 
Bronn, is into the Calcaire grossier and the Molasse, with their individual 
deposits. The principal of the other systems of classification is that of Mr. 
Lyell, adopted by most English and American geologists. Supposing the 
number of fossil shells in the entire tertiary to be accurately ascertained, 
that series of strata in which three and a half to five per cent. of the species 
are identical with living forms, is called the eocene ; a proportion of about 
eighteen per cent. of recent species constitutes the miocene; thirty-five to 
fifty, the older pliocene ; and ninety to ninety-five, the newer pliocene. A 
classification of this character, based upon the proportion in which existing 
species occur, may and does answer an excellent purpose when all the fossil 
shells have been studied and ascertained ; where this is not the case, any 
such arrangement must be liable to incessant modification. 
Fossils of the Tertiary Period. 
The infusoria play a great part in this period of the world’s history as 
well as in the preceding, as immense beds are sometimes entirely composed 
of the remains of such animals. In the Paris caleaire grossier, beds are 
found made up of minute shells, known formerly as Milliolites. They are 
now divided into many genera. These microscopic shells seem to belong 
to Rhizopoda, whose turns were arranged in an imbricated manner about 
a longitudinal axis, so that each new turn partly or entirely covered the 
older. 
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