forces ilian those involved in the gradient flow. The component of sea- 

 ward displacement causes the current to back to the left allowing the 

 local fresh water to be dissipated in the ocean. 



It is of interest to note that while the upper zone associated with the 

 outflow of a particular river can be identified, the region of influence of 

 that river can be defined. However, when the contributions from several 

 outflows are degraded into a single structure, as illustrated in these last 

 examples, the individuality of the parent river is lost. 



The ultimate fate of this upper and intermediate zone have not been 

 fully investigated, but it is remarked that in this and other local examples 

 both of these zones become more saline to seaward, while the salinity 

 of the lower zone remains constant. This implies that deep water is 

 transferred upwards, but no fresh water is transferred downwards, across 

 the boundary, and the mixing force is provided by the wind. 

 . From these and similar examples it is reasoned that fresh water can 

 only be transferred downwards in the sea by external accelerations, such 

 as the wind, or tidal convergences, and in general these are limited to 

 moderate depths. It follows that surface water remains on the surface, 

 and when removed from the influence of coastal streams the salinity of 

 the sea surface increases in the direction of flow because of progressive 

 dilution with Underlying sea-water and removal of fresh water by evapor- 

 ation. The latter process completes the cycle, since all land drainage 

 must be supplied bj^ evaporation. 



References 



(1) TuLLY, J. p. (1949) : Oceanography of Alberni Inlet. In Puh. of Bull- 



Fis. Res. Bd., Canada. 



(2) Cameron, W. M. : Oceanography of Chatham Sound. (MS. in preparation.) 



(3) TuLLY, J. P. : Oceanography of Georgia Strait. (MS. in preparation.) 



(4) • (1937) : Oceanography of Nootka Sound. /. Biol. Bd. Can., 3, (1). 



(5) Jacobson, a. W. (1948) : An Instrument for Recording Continuously the 



Salinity, Temperature, and Depth of Sea Water. Trans. Amer. Inst. Elec. 

 Eng., 67. 



(6) TuLLY, J. P. (1942) : Surface Non-tidal Currents in the Approaches to Juan 



de Fuca Strait. Journ. FisJi Res. Bd. Can., 5 (4). 



(7) Marner, PI. A. (1926) : Coastal Currents Along the Pacific' Coast of United 



States. Pub. No. 121, U.S. Coast and Geodetic Survey. 



(8) TuLLY, J. P. (1937) : Gradient Currents. Prog. Rept. Fish. Res. Bd. Can., 



No. 33, Oct. 



(9) Ford, W. L. (1947) : Distribution of the Merrimack River Effluent in Ipswick 



Bay. Tech. Rept. No. 3 on the Hydrography of the Western Atlantic, Woods 

 Hole Ocean. Inst. Aug. 



(10) RossBY, C. G. (1937) : On the Mutual Adjustment of Pressure and Velocity- 



Distributions in Certain Simple Current Systems. Journ. Mar. Res., 1, 1. 



(11) Spilhaus, a. F. (1937) : Note on the Flow of Streams in a Rotating System. 



Journ. Alar. Res., 1, 1. 



(12) TuLLY, J. P. (1935) : Kurdsio. Prog. Rept. No. 25, Fish. Res. Bd. Can. 



(13) TuLLY, J. P. ; HoLLiSTER, H. J. ; Fjarlie, R. L. I. ; and Anderson, W. 



(1949) : A Hydraulic Model of Alberni Harbour. In publication. Bull. 

 Fish. Res. Bd. Can. 



(14) TuLLY, J. P. (1937) : A Procedure for Increasing the Accuracy of Surface 



Current Charts Based on Hydrodynamic Observations. Journ. Biol. Bd. 

 Can., 3 (2). 



i ^ Summary of Discussion 



Professor Yonge indicated that in his experience a vertical salinity 

 gradient at points of entry of fresh water was not universal, and instanced 

 the Bristol Channel, which seemed to illustrate a pure mixing of a 

 horizontal wall. He admitted, however, that work don on the Tyne 



288 



