VIII THE ANTIQUITY OF MAN IN NORTH AMERICA 437 
The extensive shell heaps of the Aleutian islands have 
been carefully examined and reported on by Mr. Dali, and are 
found to exhibit some remarkable and probably unique pecu- 
liarities. Complete sections were made across several of these, 
and they were found to consist of a series of distinct layers, 
each marked by some well-defined characteristics. In the 
upper layers only are there any mammalian remains, and 
these may be divided into three subdivisions. In the upper 
bed there are found seals, walruses, etc., aquatic and land 
birds, the arctic fox and dog, with well-made weapons and 
implements, awls, whetstones, needles, and lamps. In the 
next layer the dog and fox are absent, as are remains of 
large whales ; and in the lower mammalian layer there are 
seals and small cetacea only, but no birds or land animals, 
and the weapons found are ruder. We then come to a con- 
siderable layer in which there are no mammalian remains 
whatever, but only fish-bones and molluscan shells, with rude 
knives, lance heads, etc. Below this is a bottom deposit con- 
sisting entirely of the shells of echini, and containing no 
weapons, tools, or implements of any kind, except towards 
the surface of the layer, where a few hammer stones are 
found, round pebbles with an indentation on each side for 
the finger and thumb. Echinus’ eggs are now eaten raw by 
the Aleuts, and it is the only eatable part of the animal. It 
takes forty or fifty full-sized echini for a meal. Some of the 
heaps cover five acres, and from a careful estimate founded 
on experiments, and taking the probable numbers of a colony 
which could have lived on such a spot, Mr. Dali calculates 
that it would take about 2200 years to form such an accu- 
mulation. A similar estimate applied to the upper layers 
brings the time required for the accumulation of the entire 
series to 3000 years, but that is on the supposition that they 
were formed continuously. This, however, was evidently not 
the case. Each layer indicates a change of inhabitants with 
different habits and in a somewhat different phase of civilisa- 
tion, and each such change may imply the lapse of a long 
period, during which the site was abandoned and no accumu- 
lation went on. These shell heaps may, therefore, carry us 
back to a very remote antiquity. 
