3 6 4 
FEATHERED FORMS OF OTHER DAYS. 
THE GREAT AUK (ALCA IMPENNIS). 
or otherwise, and are drowned, invariably float 
on the surface, owing to their exceedingly 
light skeleton and their feathers. Here they 
eventually reach the shore-line, where in a very 
little while their tender bodies macerate, and 
the bones are scattered far and wide, or some 
prowling animal makes still quicker work of 
them. In salt water the preservative qualities 
of that fluid, no doubt, allow them all to reach 
the shore-line with greater certainty, but here 
sun, moisture, and the carnivora of earth, air, 
and sea soon put them out of sight. 
Animals, on the other hand, often sink to 
the bottom, and, if the place of deposit be in 
a river, may soon be covered up, after lodg- 
ment, by the sediment, and thus be preserved 
for ages; but, as we have just seen, this rarely 
happens with the bodies of birds, which float 
upon the surface and are dispersed. 
As the more modern forms of birds for 
many ages have not been in the habit of re- 
sorting to caverns for any purpose, and have 
rarely been dragged in by beasts of prey, this 
fruitful source of preservation of many of the 
dead mammalia and reptiles need hardly be al- 
luded to in the case of birds. The peat-mosses, 
wherever they occur in any country, owing 
to their antiseptic qualities, have preserved 
many a form for the students of all ages ; but 
these have only allowed the heaviest of birds 
to sink into them, as the Mare aux Songes 
did the dodo in Mauritius, whereas the lighter 
