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 Faroe, I stated my belief that the current was entirely banked up in the Faroe 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 isothermal lines have a slight but uniform deflection. Within that line types characteristic of the Scandinavian 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 Acanthometrina 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 almost somewhat less than might be expected if the Gulf Stream came close to the western shore. While the communication between the North Atlantic and the Arctic Sea--itself a second _cul de sac_--is thus restricted, limiting the interchange of warm and cold water in the normal direction of the flow of the Gulf Stream, and causing the diversion of a large part of the stream to the southward, the communication with the Antarctic basin is as open as the day; a continuous and wide valley upward of 2,000 fathoms in depth stretching northward along the western coasts of Africa and Europe.