606 PALHONTOLOGICAL GEOLOGY. [Boor V. _ 
most part in limestone or in calcareous rock, their floors are 
commonly coated with stalagmite from the drip of the roof; and as 
this deposit is of great closeness and durability it has effectually 
preserved whatever it has covered or enveloped. The caves have in 
many instances served as dens wherein predatory beasts, like the 
hyzena, cave-lion, and cave-bear slept, and into which some of them 
dragged their prey. In other cases they have been merely holes 
whither different animals crawled to die, or into which they fell or 
were swept by inundations. Under whatever circumstances the 
animals left their remains in these subterranean retreats, the result 
has been that the bones have been covered up and preserved. Still 
we must admit that, afterall, only a fraction even of the mammals of © 
the time would enter the caves, and, therefore, that the evidence of 
the cavern-deposits, profoundly interesting and valuable as it is, 
presents us with merely a glimpse of one aspect of the life of the | 
land. 
e. Mineral-springs—The deposits of mineral matter resulting 
from the evaporation of mineral springs on the surface of the ground 
serve as receptacles for occasional leaves, land-shells, insects, dead 
birds, small mammals, and other remains of the plant and animal life 
of the land (pp. 354, 461). 
f. Volcanic deposits—Sheets of lava and showers of volcanic dust 
may entomb terrestrial organisms (pp. 207, 231). It is obvious, how- 
ever, that even over the areas wherein volcanoes occur and continue 
active they can only to a very limited extent entomb and preserve 
the flora and fauna of the land. 
2. In the Sea.—In the next place, if we turn to the sea, we find 
certainly more favourable conditions for the preservation of organic 
forms, but also many circumstances which operate against it. 
While the level of the land remains stationary, therecan be but little 
effective entombment of marine organisms in littoral deposits; for 
only a limited accumulation of sediment will be formed until subsi- 
dence of the sea-floor takes place. In the trifling beds of sand or 
gravel thrown up on a stationary shore, only the harder and more 
durable forms of life, such as gasteropods and lamellibranchs, which 
ean withstand the triturating effects of the beach waves, are likely to 
remain uneffaced. 
Below tide-marks, along the margin of land whence sediment is 
derived, conditions are more favourable for the preservation of 
marine organisms. Sheets of sand and mud are there laid down, 
wherein the harder parts of many forms of life may be entombed 
and protected from decay. But only a small proportion of the total 
marine fauna may be expected to occur in ‘uch deposits, At 
the best, merely littoral and shallow-water forms will occur, and 
even of these there can be no considerable proportion imbedded 
and preserved, save where a sufficiently abundant and rapid deposit 
of sediment is combined with a slow depression of the sea-bottom. 
But under the most favourable conditions they will hardly represent 
