must have come from the Gulf of Mexico, or perhaps even from California,
and the knives and pipes found in the same graves are often formed of
far-fetched material, that was naturally paid for by some home product
exported to the locality whence the material was derived. The art of
preserving fish, flesh, and fowl by drying and smoking is widely
diffused, and of great antiquity. The Indians of Long Island Sound are
said to have carried on a trade in dried shell fish with tribes residing
very far inland. From the earliest ages, the inhabitants of the Faroe
and Orkney Islands, and of the opposite mainland coasts, have smoked
wild fowl and other flesh. Hence it is possible that the animal and the
vegetable food, the remains of which are found in the ancient deposits I
am speaking of, may sometimes have been brought from climates remote
from that where it was consumed.

The most important, as well as the most trustworthy conclusions with
respect to the climate of ancient Europe and Asia, are those drawn from
the accounts given by the classical writers of the growth of cultivated
plants; but these are by no means free from uncertainty, because we can
seldom be sure of an identity of species, almost never of an identity of
race or variety, between vegetables known to the agriculturists of
Greece and Rome and those of modern times which are thought most nearly
to resemble them. Besides this, there is always room for doubt whether
the habits of plants long grown in different countries may not have been
so changed by domestication or by natural selection, that the conditions
of temperature and humidity which they required twenty centuries ago
were different from those at present demanded for their advantageous
cultivation. [Footnote: Probably no cultivated vegetable affords so good
an opportunity of studying the law of acclimation of plants as maize or
Indian corn. Maize is grown from the tropics to at least lat. 47 degrees
in Northeastern America, and farther north in Europe. Every two or three