BIOLOGICAL SURVEY OF WOODS HOLE AXD VICINITY. 33 



such analyses, while highl}- 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 IVing) stations. 



Excluding a more or less narrow adlittoral zone, the bottom area here portrayed 

 divides itself into three main regions : " 



(i) 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 dififerent tvpe 

 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 ma)- 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 algae, are frequently listed from 

 bottoms of sand or even mud. 



» These divisions do not correspoud to those recognized in the botanical section of this report. Of the latter there are five. 

 16269° — Bull. 31, pt. I — 13 3 



