BIGELOW: EXPLORATIONS IN THE GULF OF MAINE. 87 



separation from the general bottom circulation. The highest bottom 

 velocity recorded in Massachusetts Bay was .25 knots per hour. 

 The observations at Station 7 show that over the western basin oppo- 

 site Cape Ann the surface current begins to flow westerly with the 

 considerable velocity of .5 knot, at least two hours before it is low 

 water at Cape Ann; but not the bottom current, for the latter, a few 

 minutes later, was still flowing to the east, though slowly. 



There are four stations between Jeffrey's Ledge and the mainland 

 in depths from twenty -five to eighty fathoms, at which bottom as well 

 as surface readings were taken, Stations 8, 11a, on the flood; Stations 

 9, lib and c, 14, on the ebb. On the surface the flood current runs 

 to the west (Station 8), orW. by S. (11a), velocity .3 to .4 knots per 

 hour, and the three sets of observations at Station 11 show that the 

 current was still running to the westward two hours after high water at 

 Cape Ann and Cape Porpoise, though it had veered from west to north 

 by west. But there were several active tide-rips in the vicinity, which 

 were probably responsible for this apparent on-shore flow during the ebb. 

 At Station 14, there was a strong current flowing southwest (.6 knot) 

 two hours before low water at Cape Porpoise, only eight miles distant. 

 But at Station 9 it had started to run slowly to the N. E. by E. one 

 hour after, high water. On the bottom the current was easterly in 

 every case (Station 8, 9, 14, lie) except at lib, where there was a 

 very slow movement to the N. N. W. One of these records (Station 8) 

 is at four-hour flood, the others are at various stages of the ebb. At 

 Station lib, two-hour ebb, the bottom flow was toward the N. N. W.; 

 but one half hour later it had veered to the E. by N., i. e., toward the 

 extremity of Jeffrey's Ledge. At Station 14 there was a .3 knot cur- 

 rent on the bottom toward the E. by S. the surface flow being S. W. 



On Jeffrey's Bank (Station 25) the bottom current was to the E. S. E. 

 almost at right angles to the surface flow (N. by W.), three hours after 

 high water at Portland and Rockland. 



Our one bottom reading in the eastern basin (Station 27) revealed 

 a quarter-knot current, running southerly, like the surface flow, on 

 the early ebb. 



Off Cape Cod, our single reading (Station 43) showed that the 

 bottom flow was still toward the northwest, on the early ebb, although 

 the surface current was already flowing to the southeast. 



Circulation as shown by temperature and salinity. — Since we have 

 seen that the surface currents of the Gulf, though often violent, do not 

 demonstrate the existence of any circulation on broader lines than that 

 caused by the tides, we must turn to salinities, temperatures, and 



