1914] Sumner, et al.: Physical Conditions in San Francisco Bay 91 
stations were of this character, together with those from the dredging 
stations 5847 and 5848. 
The object of the analysis of these samples was twofold: (1) to 
make a quantitative determination of the physical texture of the 
various materials found in different parts of the bay, regardless of 
chemical composition, and (2) to ascertain the proportions of shelly 
matter (calcium carbonate) and of vegetable debris. To these must 
be added a third object, in the case of about sixty of the mud samples, 
namely, a determination of the total amount of nitrogen present. 
As already stated, the laboratory methods here employed were 
largely prescribed by Professor Louderback, who also, in considerable 
measure, supervised the analyses. The mode of procedure necessarily 
differed somewhat with the nature of the specimen at hand. The 
materials were classified roughly under the three following heads, 
though it will be understood that no one of these was often entirely 
free from the others. 
I. Stones and gravel—The portion chosen for study was dried, if 
necessary, then weighed. Any shells or shell fragments which might 
be present were removed and weighed separately, and the same was 
done with fragments of wood or other vegetable debris. In some eases, 
stones were scraped to remove barnacles, caleareous Bryozoa, ete. 
The size of a few of the largest stones was determined by ealiper 
measurements and by weighing. 
If, as commonly happened, the sample comprised any finer in- 
vredients, it was sifted upon a series of screens, having circular 
apertures 10mm., 5mm., and 2mm. in diameter respectively. The 
amount of the material remaining upon each screen was weighed 
separately. That passing through the two-millimeter sieve was re- 
garded as sand, and was treated as will be described below. If this 
latter contained mud the two were separated according to the pro- 
cedure employed in general for such mixtures. 
Il. Sand.—When the sample consisted preponderatingly of non- 
muddy material, fine enough to pass through the two-millimeter sieve, 
it was regarded as sand. The specimen was dried, if necessary, after 
which it was weighed. It was then passed through the above-mentioned 
series of screens, to remove pebbles, shells and vegetable debris, which 
were separated and weighed. 
If an appreciable amount of mud was present in the sand, this 
sifting was done under water in order to prevent caking and to insure 
