Evidence on the Deposition of Loess. — Owen. 299 
high stage until so late in the season that this covering of veg- 
etation fails, then the period of seolian erosion is extremely 
short; and after so long a wet season the winds are seldom 
high. The development of land snails on high lands subject 
to similar submergence and plant growth is not so much a 
mystery to be explained as a sequence to be expected. In re- 
gard to their term of life, S. P. Woodward says: 
"Land snails are mostly biennial ; hatched in summer and autumn, 
they are half grown by the winter-time, and acquire their full growth 
in the following spring and summer." 
These frail animals are known to inhabit, or infest, all 
countries save the arctic regions, to thrive in altitudes from sea 
level to seven thousand feet, and to successfully resist or defy 
extermination. Their habits of hibernation certainly gave 
them' protection against the cold of winter and their survival 
of general floods may be accounted for, possibly, in more than 
one way. It is known to naturalists that they can endure sub- 
mergence while in hibernation but the limit of such endurance 
seems not yet to have been determined. Dr. Johnson says : 
"There is something admirable in this curious adaptation of the 
economy of the hibernating creatures to their situation ; for otherwise 
they could not live beyond a single summer in the countries which they 
now inhabit with impunity to themselves. If, during their active state 
of existence, you were to keep a Limneus, or any other aquatic pul- 
moniferous species, immersed in water for only one short day, or even 
for little more than an hour, it would die irrecoverably; but it remains 
under water, perhaps with the surface frozen over, for three or four 
months uninjured, when the system has been prepared in autumn for the 
change. And so of the land kinds ; they perish if deprived of air for 
a few hours only in summer, or if exposed to an artificial cold not lower 
than the cold of winter ; but in a state of hibernation tney respire, if any, 
such a small quantity of air as not to be appreciated, and brave our 
longest and severest frosts without peril and without pain." 
Many may have also survived among the uprooted willows 
and other growths that may be seen floating as rafts on a Mis- 
souri flood, and soon anchored in masses to a stranded tree or 
snag. Large quantities of eggs might also be carried short 
distances in nests held securely among the fibrous roots. Roots 
of any considerable size float above the water. 
The question of sustenance is an even more simple one to 
dispose of when we consider that snails are by no means fastid- 
ious and actual starvation is not a serious menace. Of diet Dr. 
