Biological Succession in Aleutians — Bank 
terfered with normal plant succession. During 
volcanic eruptions, for instance, large areas 
were completely covered by ash, and the vege- 
tation was thus exterminated. Major ash falls 
are clearly marked in the soil profiles (Fig. 2). 
A number of such ash falls must have origi- 
nated from violent eruptions which gradually 
diminished to a rather continuous, compara- 
tively quiet eruption of long duration. The 
results of this activity appear in the profile 
as layers composed of coarse pumice overlaid 
by ash which becomes increasingly finer to- 
ward the top. These deposits are often 0.5 
meters or more thick and are almost pure 
volcanic material devoid of any organic re- 
mains. Frequently they separate layers of al- 
most pure humus (Fig. 3). The vegetation 
was destroyed by the ash fall and had to 
reinvade the area, in time producing the over- 
lying humus. Thus, it is somewhat possible 
in the Aleutians to follow both the volcanic 
history and the major accompanying disrup- 
tions in plant succession. 
Pollen studies of humus intercalated be- 
tween ash strata offer one method of arriving 
at a history of postglacial plant succession, 
and for this purpose hundreds of soil samples 
were secured from various ash profiles and 
archaeological sites. Several of these samples 
have already been examined briefly for pollen 
by S. T. Anderson, and a preliminary report 
of the results has been released (Anderson 
and Bank, 1952). These are interesting and 
worth summarizing. Two humus samples 
from soil strata, one at 0.92 meters depth 
and the other at 1.83 meters depth, came from 
a single ash profile on Tanaga Island in the 
middle Aleutians. Usually, terrestrial ash-soil 
deposits should not contain much pollen, as 
the grains would ordinarily be destroyed by 
oxidation. It was therefore somewhat surpris- 
ing to find that these samples contained suf- 
ficient pollen for quantitive studies. This is 
probably because of the unusual Aleutian 
climate, marked by consistently high precipi- 
tation and fairly low soil temperatures. Many 
Aleutian soils are constantly saturated with 
497 
water, which undoubtedly is a major factor 
in the preservation of pollen and spores. 
The samples were treated according to the 
procedure described by Faegri and Iversen 
(1950). Pollen from the lower part of the 
profile represents an entirely different plant 
community from that of the upper part. The 
Fig. 3. Diagrammatic profile at the edge of an Aleut 
kitchen midden on Nazan Bay, Atka Island. Vertical 
and diagonal cross-hatching indicates clam shell, fish 
bone, and sea urchin shell deposits (archaeological). 
Also shown are sea lion bones and a stone lamp in 
position. The nonarchaeological strata are:' A, recent 
humus; B, sand; c,E,i, fine ash, slightly stratified; 
D,G,K, humms with fine ash admixture, stratified; F, 
H,J, coarse pumiceous ash; L, brown clay with large 
pumice (till ?); m, bedrock; 1,2,3, ferruginous bands 
(from leaching from above?). Surface vegetation, es- 
pecially lush on such sites, is indicated and includes: 
Heracleum lanatum, Elymus arenarius subsp. mollis^ Co- 
nioselinum Gmelini, Angelica lucida, Aconitum maximum, 
Claytonia sibirica, Achillea borealis, and Calamagrostis 
canadensis var. Langsdorffii. 
