BIOLOGICAL SURVEY OF WOODS HOLE AND VICINITY. 29 



which penetrate deeply into the mainland. Some of these, as will be shown later, 

 furnish considerable quantities of fresh water at certain times of the year. The depth 

 of Buzzards Bay beyond the "adlittoral" zone (see p. 179) ranges from 3 fathoms near 

 its head to 18 or more fathoms at its mouth. About a mile west of Penikese Island 

 occurs a deep hole only recently charted. Here a depth of 24 fathoms has been found, 

 this being, so far as known, the deepest sounding obtainable within a distance of 10 miles 

 or more from land. Throughout most of its extent, however. Buzzards Bay is much 

 shallower than Vineyard Sound, and a depth of 10 fathoms is seldom or never encoun- 

 tered except near its lower end. 



The conditions existing in Buzzards Bay and Vineyard Sound can not be understood 

 without reference to the adjacent features of the coast and the ocean. The tidal cur- 

 rents, as well as the character of the water, are doubtless influenced by the proximity 

 to the westward of Narragansett Bay and Long Island Sound. From the mouth of 

 Vineyard Sound the Atlantic Ocean, throughout an arc of about 120°, extends for an 

 indefinite distance uninterrupted either by land or by shoals. The depth, on the whole, 

 increases very gradually, the "continental shelf" extending out to a distance of over 

 75 miles to the southward of Gay Head, where the loo-fathom line is encountered. 

 Shortly thereafter an abrupt descent commences. South of Marthas Vineyard the 

 20-fathom line lies 10 miles or more off shore, and the distance increases as we pass to 

 the westward. South of Narragansett Bay, however, it sends a long slender loop in a 

 northeasterly direction toward the mouth of Vineyard Sound, reaching a point within 

 about 6 miles of Gay Head. 



To the east and southeast of Woods Hole the geographical conditions are peculiar, 

 and are highly important in determining the nature of the fauna and flora on this part 

 of the coast. The peninsula of Cape Cod, together with the two large islands to the 

 southward, inclose a broad, shallow body of water — Nantucket Sound. This attains a 

 high temperature during the summer months, and doubtless in large degree influences 

 the temperature of \^ineyard Sound, with which its waters mingle freely as a result of 

 tidal currents (p. 36). It is possible, also, as has been held by certain writers, that Cape 

 Cod, together with Nantucket and its associated shoals, constitute a barrier which 

 deflects a well-defined cold ocean current away from the mainland of the continent. 

 Whether or not this is true, it is an undoubted fact that the coastal water temperatures 

 to the east and north of Cape Cod are much lower during the summer months than 

 are those immediately to the south of it. The resulting faunal differences will be dis- 

 cussed elsewhere, and the temperature conditions \\ill likewise be considered more fully 

 in another place. 



2. CHARACTER OF THE SHORES AND BOTTOMS. 



The dominant feature of the shores and bottoms along this section of the coast is 

 the glacial debris. Although the main outlines of the land topography of this region 

 may be preglacial, as Shaler (1898) contends, there are extensive morainal deposits 

 upon Nantucket, Marthas Vineyard, and the Elizabeth Islands, as well as on neighboring 

 parts of the mainland. Indeed, a large part of the local shore line and sea bottom still 

 consists of practically unaltered glacial boulders and gravel, which have been subjected 

 for only a comparatively brief period to erosion and transportation by waves and cur- 

 rents. Even the Middle Ground in Vineyard Sound is regarded by Shaler as "a bit of 



