10 EXTINCT MONSTERS. 
have undergone very little change, and have, as it were, been 
simply sealed up. The state of a fossil depends on several cir- 
cumstances, such as the soil, mud, or other medium in which it 
may happen to be preserved. Again, the newest, or most recent, 
fossils are generally the least altered. We have fossils of all ages, 
and in all states of preservation. As examples of fossils very 
little altered, we may take the case of the wonderful collection of 
bones discovered by Professor Boyd Dawkins in caves in various 
parts of Great Britain. The results of many years of research 
are given in his most interesting book on Cave-Hunting. ‘This 
enthusiastic explorer and geologist has discovered the remains of 
a great many animals, some of which are quite extinct, while 
others are still living in this country. ‘These remains belong to a 
late period, when lions, tigers, cave-bears, wolves, hyzenas, and 
reindeer inhabited our country. In some cases the caves were 
the dens of hyzenas, who brought their prey into caverns in 
our limestone rocks, to devour them at their leisure; for the 
marks of their teeth may yet be seen on the bones. In other 
cases the bones seem to have been washed into the caves by old 
streams that have ceased to run; but in all cases they are fairly 
fresh, though often stained by iron-rust brought in by water that 
has dissolved iron out of various rocks—for iron is a substance 
met with almost everywhere in nature. Sometimes they are 
buried up in a layer of soil, or ‘‘cave-earth,” and at other times 
in a layer of stalagmite—a deposit of carbonate of lime gradually 
formed on the floors of caves by the evaporation of water charged 
with carbonate of lime. 
Air and water are great destroyers of.animal and vegetable 
substances from which life has departed. ‘The autumn leaves 
that fall by the wayside soon undergo change, and become at last 
separated or resolved into their original elements. In the same way 
when any wild animal, such as a bird or rabbit, dies in an exposed 
place, its flesh decays under the influence of rain and wind, so that 
before long nothing but dry bones is left. Hamlet’s wish that 
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