1896.] Fossils and Fossilization. 1001 
hood of general destruction from other causes of the fish in 
geological strata, wherein they abound, make it a useful point 
of reference in this matter. Nordenskiold says (Voyage of the 
Vega), “a large number of fish (Gadus polaris) were seen above 
the foot of a large block of ground ice, near which we lay to 
for some hours. Next day we saw near one of the islands, 
where the water was very clear, the sea-bottom bestrewed with 
innumerable fish of the same species. They had probably 
perished from the same cause, which often kills fish in the 
river Obi in so great numbers that the water is infected, 
namely, from a large shoal of fish having been inclosed by 
ice in a small hole, where the water, when its surface has 
frozen, could no longer by absorption from the air replace the 
oxygen consumed, and where the fish have thus been literally 
drowned. 
However accumulated, whether by the sudden death of 
large numbers of animals by floods and storms along the 
banks of streams or the margins of lakes, or whether 
from other natural causes animals perish in numbers and 
upon restricted areas, their bones are carried by water action 
into the depressions, sinks, crevices and basins of a country, 
and being there sealed up from decomposition or dispersion by 
the silt and gathering accretions of various mineral deposits 
above them, they become fossils. The caves in limestone dis- 
tricts receive a contribution of animal remains partially 
brought into them by surface water partially by the the pred- 
atory instincts of carnivorous mammalia or birds. Prof. Hartt 
in his Geology of Brazil instances the interesting examples in 
the Sao Francisco basin wherein the numerous caverns, ex- 
tending sometimes two thousand feet into the rock, furnish 
abundant remains both of long extinct mammalia as the Glyp- 
todon, Mastodon, Mylodon, Megatherium, Chlamydotherium, 
Toxodon and Macrauchenia, and innumerable remnants of 
the smaller living animals brought there by owls, whose bones 
mingle with those of other occupants, as bats and felide. 
These variously distributed in the different caves were mingled 
in a red clay earth more or less cemented and encrusted by a 
stalagmitic crust. Similarly fossil vertebrates have been en- 
tombed in the caves of England, France, Belgium, Spain, 
