1914] Sumner, et al.: Physical Conditions in San Francisco Bay 95 
by these preliminary studies, have been represented in plates 5, 6, 
and 7. 
Plate 5 is based upon the samples taken with the dredge, together 
with the upper (surface) sections of the tube samples. The number 
of circles upon this chart, representing stations, will be found to be 
less than the number of stations included in the table giving the results 
of our analyses. While there are seventy-nine of the latter, only sixty- 
four of the former have been plotted. This has resulted from two 
causes: (1) the character of the bottom at certain of the stations 
is Inadequately represented in the tables, for reasons which have just 
been explained; (2) certain of the stations, particularly in the central 
region of the bay, were very close together or actually intersected 
one another. Thus the symbols representing the bottom character 
at these stations would have overlapped considerably had not some of 
these been omitted. In a few other cases, overlapping has been 
avoided by a slight shifting apart of two of the symbols. In general, 
the center of the circle represents the position of the station, or, in 
the case of a dredge-haul, the middle point of the line traversed. 
In these symbols, percentages by weight of the various-sized par- 
ticles have been indicated by the relative areas of the sectors. The 
finest dots designate sand (1.e., particles less than two millimeters in 
diameter, but coarser than mud), the next larger ones represent par- 
ticles two to five millimeters in diameter, the next five to ten, and the 
largest ones particles over ten millimeters. Mud is represented by 
the uniformly black areas. In constructing these sectors, no ingredient 
was included unless it represented three per cent or more of the total, 
i.e., there are no sectors of less than eleven degrees. 
In the report upon the biological survey of the Woods Hole region 
(see Sumner, Osburn, Cole, and Davis, 1913), bottom characters were 
represented by a similar system of circles divided into variously 
shaded sectors. There, however, no quantitative study was made of 
the various ingredients, so that the sectors did not represent per- 
centages. 
Since the adoption of the system of symbols employed in the 
present report, our attention has been called to another work, in 
which the actual proportions of the ingredients have been represented 
by sectors of various sizes. The system of shading does not, however, 
agree with that adopted here (see Hiilsen, 1912). 
Since calcium carbonate appeared in any or all of the screenings, 
the proportion of this material in a given sample plainly cannot be 
