BIGELOW: EXPLORATIONS IN THE GULF OF MAINE. 89 



range of temperature from surface to bottom at successive stations 

 along the coast from the Penol)scot to Grand Manan, the surface 

 growing warmer, and the bottom colder at least at corresponding 

 depths, is evidently due to the fact that the diminishing force of the 

 tidal currents is less and less effective in causing vertical circulation, 

 so that the waters retain more and more nearly their normal tempera- 

 ture gradient. Exactly the opposite takes place in passing off shore 

 from the mouth of Grand ^Slanan Channel, the temperature and salin- 

 ity range growing progressively greater. 



The mouth of Casco Bay, i. e., the region where the general trend 

 of the coast changes from northerly to northeasterly, is the dividing 

 line between temperature sections of two types; for whereas the 

 coast waters east of this point were about as much warmer than the 

 off-shore stations on the bottom as they were colder on the surface, the 

 coast water south and west of Portland was no warmer on the bottom 

 than it was off Cape Ann or near Piatt's Bank, though it was constantly 

 several degrees colder on the surface. On the contrary, Station 11, 

 close to the coast, was colder at all depths down to about sixty fathoms 

 than the water east of Jeffrey's Ledge, and the curve at Station 14, 

 off Cape Porpoise, was almost precisely like it, the same temperatures 

 being found from five to ten fathoms nearer the surface at Station 11 

 than at Stations 23 and 24. Below fifty fathoms the temperatures 

 were about equal. If temperature were the only clue to oceanic circu- 

 lation, we would naturally assume that such a profile indicated an 

 upwelling of cold bottom water. But the salinities of this region, 

 forbid this explanation, because, as the salinity sections show, the 

 in-shore stations were fresher at all depths, whereas, if the surface were 

 cooled by water rising from below, the salinity would necessarily be 

 raised by the same process, and we would expect to find the surface 

 Salter than, or at least as salt as it was at the stations further off shore. 

 But although the temperature readings at Station 11 were lower at all 

 depths down to fifty fathoms, than they were east of Jeffrey's Ledge, 

 the curve for the former wa3 almost precisely the same as it was at 

 Station 2, in the mouth of ]\Iassachusetts Bay a few days earlier, 

 except that the upper ten fathoms were cooler at Station 1 1 ; while the 

 salinity curves (fig. 11) show that the latter was slightly salter than 

 Station 2 at the surface, slightly fresher below thirty fathoms. It is 

 evident that while vertical movements of such a column of water as 

 was met at Station 24 could not reproduce the temperature and 

 salinity conditions found at Station 11, a vertical mixing of the upper 

 fifteen or twentv fathoms of the waters at Station 2 would cause 



