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400 THE DEPTHS OF THE SEA. [CHAP. VIII. 
return currents are very visible on the chart taking 
this direction, indicated by marked deflections of 
the iscthermal lines. The most marked is the 
Labrador current, which passes down inside the 
Gulf-stream along the coasts of Carolina and New 
Jersey, meeting it in the strange abrupt ‘cold 
wall,’ dipping under it as it issues from the Gulf, 
coming to the surface again on the other side,. 
and a portion of it actually passing, under the Gulf- 
stream, as a cold counter-current into the Gulf of 
Mexico. 
Fifty or sixty miles out from the west coast of 
Scotland, I believe the Gulf-stream forms another, 
though a very mitigated, ‘cold wall.’ In 1868, 
after our first investigation of the very remarkable 
cold indraught into the channel between Shetland and 
Froe, I stated my belief that the current was entirely 
banked up in the Fwroe Channel by the Gulf-stream 
passing its gorge. Since that time I have been led 
to suspect that a part of the Arctic water oozes down 
the Scottish coast, much mixed, and sufficiently 
shallow to be affected throughout by solar radiation. 
About sixty or seventy miles from shore the isother- 
_mal lines have a slight but uniform deflection. 
Within that line types characteristic of the Scandi- 
navian fauna are numerous in shallow water, and 
in the course of many years’ use of the towing net 
I have never met with any of the Gulf-stream 
pteropods, or of the lovely Polycystina and Acantho- 
metrina which absolutely swarm beyond that limit. 
The difference in mean temperature between the 
east and west coasts of Scotland, amounting to 
about 1°C., is also semewhat less than might be 
