BIOLOGICAL SURVEY OF WOODS HOLE AND VICINITY. 33 
such analyses, while highly valuable as studies in mineralogy, would not alone give a 
fair idea of the respective bottom areas considered as the habitats of living beings. 
The chart showing bottom characters represents rather crudely the condition of the 
floor of Buzzards Bay and Vineyard Sound, certain conventional modes of shading 
being adopted to represent the chief ingredients. The circles having a composite shading 
are commonly divided into equal halves or thirds, as if the various constituents were 
present in equal amounts. “This results from the imperfections, in this regard, of the 
records upon which this chart is based. In the plotting of these circles, likewise, it has 
been necessary to adjust the position of each to that of its neighbors, with the result that 
in certain cases the symbol is removed some distance from the bottom designated. This 
is particularly true of the adlittoral (Phalarope and Blue Wing) stations. 
Excluding a more or less narrow adlittoral zone, the bottom area here portrayed 
divides itself into three main regions: @ 
(1) Vineyard Sound, from its eastern end to a transverse line of division passing 
at a level somewhere between Tarpaulin Cove and Robinsons Hole. Here the pre- 
dominant feature is the presence of gravel and stones. This area, it is true, contains 
one extensive shoal of sand, the so-called Middle Ground, and many other sandy areas. 
In the bays mud likewise occurs. 
(2) Vineyard Sound from the line above referred to to its western end. Here the 
bottom is predominantly sandy, though gravel, stones, and mud occur in places. The 
presence of shell beds does not, of course, exclude the occurrence of an underlying bottom 
of sand. 
(3) Buzzards Bay as a whole. Here mud predominates, except close to the eastern 
shore, and at the extreme lower end. The latter might be regarded as an independent 
area, but it seems scarcely large enough to warrant this. 
The inshore (adlittoral) dredgings reveal in many cases a distinctly different type 
of bottom from that of the adjacent deeper waters; and various restricted areas of one 
or another kind of bottom may be found almost anywhere. 
Owing to the methods employed, it is evident that the correlation of bottom charac- 
ters with the distribution of species can be indicated with only rough approximation. 
During a given haul the dredge passes over a considerable stretch of sea floor and may 
collect samples of several totally different sorts of material. Organisms may likewise be 
collected from all points in this path. To determine by such means the kind of bottom 
proper to every species encountered is obviously impossible. A species may appear in 
the records as coming from ‘‘sand,”’ whereas it may have been scraped from the surface 
of large stones at any point during the haul. Only the broader correspondence between 
the larger areas in which certain types of bottom predominate, and the general dis- 
tribution of the species in question, is commonly to be regarded as significant. Again, 
when certain organisms are listed from certain types of bottom, the inference must not 
always be drawn that such bottoms themselves constitute its true habitat. Thus 
encrusting Bryozoa, which occurs upon shells, or alga, are frequently listed from 
bottoms of sand or even mud. 
a These divisions do not correspond to those recognized in the botanical section of this report. Of the latter there are five. 
16269°—Bull. 31, pt. 1—13 
2 
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