422 
BULLETIN OF THE BUREAU OF FISHERIES 
for 10 days at a temperature of 70° C. The drying was carried out at 70° rather 
than at 100° or higher in order to avoid the possible loss of carbonaceous material, 
especially of any volatile oils that might be present. The moisture content ranged 
from 1.43 to 5.19 per cent of the weight of the undried material in the various samples. 
The character of the water in these three lakes is indicated in the analyses given 
in Tables 8 and 9. There is a comparatively small amount of fixed or bound carbon 
dioxide present and relatively small amounts of calcium, magnesium, and silica. 
The water, therefore, may be regarded as having a medium hardness. It might be 
better, in fact, to class them as soft-water lakes. They are certainly at the lower 
limit of the class with medium hardness. 
The results of the analyses of the bottom deposits are given in Table 1 1 . One of 
the striking features of these bottom deposits is the large percentage of silica found in 
them; this substance comprises from 60 per cent to a little more than 73 per cent 
of the dry material. Such high percentages of silica raised a question regarding 
its source and portions of the various samples were submitted to Dr. Albert Mann 
who examined them for diatom remains. He found the shells of 67 different species 
of diatoms in these bottom deposits. His estimates of the percentages of diatoms in 
the various samples from Karluk Lake, based upon his microscopical examination, 
show a rather striking similarity to the results obtained in the chemical analyses. 
His statement regarding the sample from station 3 of Karluk Lake is “nearly pure 
diatoms, 80 to 90 per cent of the mass.” The 40-meter sample from The Thumb is 
estimated as 60 per cent or more diatoms, and the 125-meter sample from station 1 
of Karluk Lake as 75 to 80 per cent. He states that diatoms are not so abundant in 
the samples from Thumb and O’Malley Lakes (20 to 30 per cent), but the percentage 
of silica is the same in them as in those from Karluk Lake. No explanation of this 
difference is evident from the data in hand. (See Doctor Mann’s report on p. 434.) 
There is almost a twofold difference in the percentage of iron in the various 
samples and likewise almost a fourfold difference in the percentage of alumina. The 
calcium and magnesium content of these bottom deposits is small and the same is 
true of the phosphorus, sulphate, and carbon dioxide. The percentage of organic 
carbon shows a little more than a fourfold difference. The largest percentage was 
found in the sample from O’Malley Lake. Large aquatic plants grow much more 
abundantly in this lake than in the other two, and it seems probable that they make 
an important contribution to the bottom deposits here and thus increase the amount 
of organic carbon therein. 
In comparison with the results obtained on other lakes, the high percentage of 
silica is the outstanding characteristic of the bottom deposits of these three Alaskan 
lakes. Bottom material from two of the lakes of northeastern Wisconsin yielded a 
little more than 42 per cent of silica and this is the largest percentage that has been 
found in any of the Wisconsin lakes up to the present time. A maximum of 54 per 
cent was found in one sample from Lake Balaton, Hungary (Emszt 1911), and a 
little over 36 per cent was the largest amount found in the bottom deposits of the 
lakes at Lunz, Austria (Mulley, 1914). Halbfass (1923) reports a maximum of 78 
per cent of silica in Lake Girotte and 74 per cent in Lac Pavin. 
The small percentage of calcium is also an important characteristic of the de- 
posits of these Alaskan lakes. Smaller percentages have been obtained only in the 
very soft water lakes of northeastern Wisconsin. Less than 1 per cent of calcium 
has been found in 4 of these soft-water lakes, and from 1 to almost 2 per cent in 8 
