MARINE MOLLUSKS — MACGINITIE ^1 



shallow, barren lagoon extending along the coast southeast of the 

 Point. 



The beach at Point Barrow base consists largely of fine gravel, with 

 an occasional narrow strip of sand or admixture of sand and gravel. 

 The gravel extends out to a depth of 10 to 20 feet. This gravel zone 

 is succeeded by the mud zone of fine, blue, sticky mud, so tenacious 

 that clam shells such as Macoma have to be scrubbed individually 

 to free them of mud. A dredge haul from this zone cannot be washed 

 by dragging the dredge behind the boat; the mud has to be worked 

 over by hand for its contained specimens. At a depth of about 100 

 feet, the mud zone is replaced by the rubble zone in which the bottom 

 may be covered by pebbles and stones from the size of a walnut to 

 small boulders. The bottom in the rubble zone is rather spotty, for 

 there may be areas of mud or of gi-avel much beyond the depth of 

 100 feet, or there may be admixtures of mud, gravel, and stones in 

 about equal quantity or in any proportion. Mud areas in the rubble 

 zone consist of mud that is much less sticky than that of the mud 

 zone. 



About 12.1 miles from shore G. E. MacGinitie (1955, p. 71) dis- 

 covered a canyon about a quarter of a mile across, the bottom of 

 which (at dredging station 32) was 741 feet deep. On the shoreward 

 side of this canyon the floor of the ocean was at a depth of 438 feet 

 and on the oceanward side it was 522 feet deep. The bottom of this 

 canyon was covered with mud and a mass of worm tubes, largely of 

 Pista maculata. 



Stations in the rubble zone are subject to almost yearly change, 

 brought about by the deposition of mud from eroding shores. When 

 the ice goes out and remains far offshore as it did in the summers of 

 1949 and 1950, wind storms create high surf with consequently greater 

 erosion alongshore than when floating ice remains near shore as it did 

 during the entire summer of 1948. Floating ice tends to dampen the 

 effect of wind on waves and surf. 



The reader should bear in mind that there are no tidal zone animals 

 at Point Barrow. Usually in October, ice begins to form alongshore 

 and the ocean freezes over out to a distance of several miles and 

 seldom breaks up and leaves before about July 20. The tide appar- 

 ently does not exceed 6 inches, although there may be wind tides of 

 3 feet or more during storms. Hence, the only "shore collecting" 

 consists of gathering any specimens that may be washed ashore during 

 storms in summer and early autumn. During the summer of 1948, 

 almost no animals were washed ashore. 



Even in summer the molluskan species at Point Barrow seldom 

 experience a temperature above freezing, for the freezing point of salt 

 water is lower than 32° F. 



