124 PROCEEDINGS OF THE BOSTON MEETING 



and both dredge and core samples were taken by the staff of the United States 

 ;Steamer Albatross. Some preliminary charts and physical data have already 

 been published in a University of California Publication, Zoology, in volume 

 14, number 1, 1913. Bottom samples vary from black mud, which is especially 

 abundant in the southern part of the bay, to coarse boulders in the Golden 

 Gate. Part of this latter region appears to be kept practically free from 

 sediment by current action, and to have bedrock exposed. Parts of the bay 

 show rhythmic banding in thin layers, as seen in core samples; some parts 

 show thicker uniform layers, and some parts material not well sorted. The 

 present horizon of deposition varies in depth below sealevel from to 378 

 feet, and if preserved in the geological series would probably give the appear- 

 ance of a marked disconformity, although the wide and deep "eroded" 

 channel is contemporaneous with the deposits at higher levels now forming 

 on both sides. Considerable areas where mud is now depositing formerly 

 showed sand on which oysters and other shellfish lived. The cause of the 

 change is not understood. In core samples from these areas alternations of 

 sand and mud were found, and the appearance of a sand layer gave rise 

 immediately, as it were, to a colony of oysters that disappeared with the first 

 appearance of a mud layer. 



The distribution of types of sediment is the reverse of that ordinarily 

 given in general descriptions of sediments, in that the muds are deposited 

 inshore, often up to and including the beach, while sands are deposited farther 

 from the land and out into the ocean. 



Presented without notes. 



Dtscussioin" 



Dr. E. W. Shaw : The fact that sedimentary deposits show infinite variety 

 in mechanical constitution — no two specimens are exactly alike and there is 

 almost no semblance of natural grouping — does not seem to me a strong argu- 

 ment against classifying and naming. This argument would not be advanced 

 against the sorting of oranges or against the sizing of coal and the naming 

 of the various separates. Incidentally, the names that have become popular 

 seem to indicate that to be useful and used names must be mnemonic, 

 whether or not they are sensible. Pea coal does not resemble peas in size 

 or shape any more than in color. 



Lateral variations of strata, such as Professor Louderback describes, raise 

 a question concerning the interpretation of ancient sediments. To what 

 extent is the fact that present deposits seem to show much greater variability 

 than ancient deposits due to unusual present conditions, and to what extent 

 to mistake in correlation of ancient strata and formations? Present deposits 

 seem to vary from place to place, ancient deposits from time to time. How 

 often can we say of ancient strata, as we can of the present deposit at San 

 Francisco, "This stratum represents the various products of erosion of a cer- 

 tain fraction of an epoch. Here is the gravel, there the sand, and beyond 

 is the mud. Here is the silica, there are the oxidized and hydrated silicates, 

 and somewhere else are the carbonates, sulphates, chlorides, etcetera." 



