92 University of California Publications in Zoology [Vou. 14 
that all of the mud should pass through the finest screen. Each lot 
of material retained by the larger screens was dried and weighed. 
That which passed through the two-millimeter screen was used 
for certain further determinations. Except in the case of mud-free 
material, one portion was washed in order to separate the mud from 
the sand, another was tested for calcium carbonate. 
For the former operation, a small quantity, usually 10 oms., was 
placed in a small narrow jar, and shaken violently with a definite 
quantity of distilled water. After settling for a number of seconds, 
depending on the character of the sample, the water was siphoned 
off, down to a definite level, and the jar filled and shaken again. The 
process was repeated until the water quickly ceased to be turbid and 
the sediment consisted of particles over 50 microns in diameter. (This 
last was determined roughly by microscopic examination). The 
washings were saved for future studies upon the mud. The sand was 
dried and weighed. 
Two methods were employed in determining the calcium carbonate. 
In the case of mud-free samples, the material was weighed before 
and after extraction with HCl, it being assumed that the material 
dissolved consisted chiefly of shelly matter. 
In the ease of samples containing mud, a small portion (commonly 
10 ems.) was taken and carefully weighed. An exactly weighed 
amount of HCl was added and the loss due to the escape of gas 
(chiefly CO.) was determined gravimetrically. The amount of calcium 
carbonate originally present could readily be computed from the loss 
of CO,, allowance being made for a certain amount of the latter which 
remained in solution in the liquid. 
Both of these methods involve a certain error, namely, the assump- 
tion that whatever was dissolved in hydrochloric acid, with the 
liberation of gas, consisted of caleium carbonate. While the error 
is not believed to be very great proportionally, its magnitude is not 
known. 
III. Muds.—Samples were regarded as muds which consisted 
predominantly of material that remained in suspension for consid- 
erable periods in water. (See above). Since practically all of the 
muds contained a certain percentage of sand, and frequently of shells 
and pebbles as well, the method of treatment was much the same as 
that already described for the sand, the only difference depending 
upon the smaller proportion of coarser ingredients which were en- 
countered. The calcium carbonate was determined by the second of the 
methods above deseribed. 
