302 REPORT OF COTIMISSIONER OF FISH AND FISHERIES. 



water and high water, nor the relative duration of the ebb and flow are 

 coincident, very powerful currents set through the passages, between, 

 the Elizabeth Islands, connecting these two bodies of water. This is 

 most noticeable in the case of Wood'i^ Hole, because there the channel 

 is narrow and shallow, and much obstructed by rocks. These channels 

 are, therefore, excellent collecting grounds for obtaining such animals 

 as prefer rocky bottoms and rai#lly flowing waters. 



The shores of Vineyard Sound and Buzzard's Bay are quite diversified 

 and present nearly all kind of stations usually found in corresponding 

 latitudes elsewhere, except that ledges of solid rock are of rare occur- 

 rence, but there are numerous prominent points where the shore con- 

 sists of large rocks or boulders, which have been left by the denuda- 

 tion of deposits of glacial drift, forming the cliffs along the shores. 

 Sandy beaches are frequent, and gravelly and stony ones occasionally 

 occur. Muddy shores are less common and usually of no great extent. 



In Buzzard's Bay the bottom is generally muddy, except in very 

 shallow water about some of the islands, where patches of rocky bot- 

 tom occur, and opposite some of the sandy beaches where it is sandy 

 over considerable areas. Tracts of harder bottom, of inud or sand, 

 overgrown with algje, occasionally occur. In Vineyard Sound the bot- 

 tom is more varied. It is sandy over large districts, especiallj' where 

 the shoals occur, and in such places there are but few living animals, 

 though the sand is often filled with dead and broken shells, but in 

 other localities the sand is more compact and is inhabited by a peculiar 

 set of animals. Other extensive areas have a bottom of gravel and 

 small stones and broken shells; on such bottoms animal life is abun- 

 dant, and the entire bottom seems to be covered in some places by sev- 

 eral kinds of compound ascidiaus, which form large masses of various 

 shapes, often as large as a man's head. In still other places, chiefly off 

 rocky points and in the channels between the islands, rocky bottoms 

 occur, but they are usually of small extent. Muddy bottoms are only 

 occasionally met with. They occur in most of the deep areas which are 

 isolated, and sometimes in the deep channels, but are more common in 

 sheltered harbors and coves. 



In Nantucket Sound and Muskeget Channel the bottom is almost 

 everywhere composed of sand, and the same is true of an extensive 

 area to the east and northeast of ii^antucket Island, where shoals of 

 moving sand are numerous and often of large size, but in the i^artially 

 sheltered area on the north side of ISTantucket, there is more or less- mud 

 mixed with the sand. 



For greater convenience the following subdivisions have been adopted 

 in describing the animals of the bays and sounds : 



1. Eocky shores, between high- water and low-water marks. 



2. Sandy and gravelly shores. , 



3. Muddy shores and flats. 



4. Piles of wharves, buoys, &c. 



