1914] Sumner, et al.: Physical Conditions in San Francisco Bay 93 
In the case of the tube samples, sections about 10 em. lone were 
removed at two or more levels in these cylindrical masses of mud. One 
was taken at the top, another commonly at the bottom, while in most 
cases a third was taken from an intermediate level. This came from 
a point about midway between the two ends, unless features in the 
stratification of the deposit rendered it desirable to take the sample 
from another level. In a few instances four sections were removed. 
Each of these sections was divided longitudinally into quarters. 
One of these quarters was subjected to the treatment accorded to other 
mud samples, a second was sent to the United States Bureau of Chem- 
istry for the determination of nitrogen, a third was reserved for biologi- 
eal examination, while the fourth was retained for further possible 
mineralogical studies. 
Commonly the longer of the two tube samples taken at a given 
station was employed in these studies but both of them were opened 
and examined by Professor Louderback, notes being made by him on 
the original and final length?’ of the total sample, and of interesting 
features in its stratification. 
The results of these sifting and weighing operations together with 
the calcium carbonate determinations are presented in Appendix III. 
Here are given the absolute and percentage values of the particles of 
various sizes. In the columns headed ‘‘Gross Weight’’ these values 
are quite independent of the composition of the various particles. 
Fragments of shell have been thrown together with sand grains or 
pebbles of the same size. 
Reference to the ‘‘CaCO,”’ columns, however, shows us the absolute 
and relative amounts of shelly material in each grade of the screenings, 
so that the proportion of the inorganic particles in each may readily 
be obtained. 
For all the coarser grades (over two millimeters) the figures for 
“calcium carbonate’’ 
and shell fragments. They are, therefore, doubtless somewhat too 
high, since mollusean shells contain a certain percentage of the organic 
substance conchiolin. In old fragments, however, such as those which 
chiefly are found in bottom deposits, it is likely that most of this 
represent merely the dry weight of the shells 
organic matter has disappeared. 
25 The first was determined by measuring the distance between the two 
corks, the second was the actual length of the mud after the shrinkage due to 
evaporation. The former figure probably exaggerated, in some eases, the orig- 
inal length of the sample, since the upper cork may from the first have failed 
to reach the surface of the mud. The dry (or partly dry) measurements are 
necessarily the ones considered in the tables and charts, where sections of the 
tube samples from various levels are designated. 
