314 Tim DEPTHS OF THE SEJ. [chap. vii. 



47, 90, 49, 50, and 51, are in the warm area. There 

 is no great difference in depth between the two series 

 of soundings ; and there is no indication of a ridge 

 separating them. The only possible explanation of 

 these two so widely different submarine climates, 

 existing apparently under the same circumstances 

 and in close proximity to one another, is that the 

 Arctic indraught which passes into the deeper part 

 of the Eseroe Channel is banked in at its entrance, 

 by the warm southern stream slowly passing north- 

 wards. There is a slight but very constant depres- 

 sion of the isothermal lines of surface temperature 

 in the shallow water along the west coast of Britain. 

 This, I believe, indicates that a portion of the cold 

 Pseroe stream makes its escape, and, still banked in 

 close to the land by the warm water, gradually makes 

 its way southwards, so mixed and diluted as only to 

 be perceptible by its slight effect on the lines of mean 

 temperature. Diagrams 55 and 56 illustrate the dis- 

 tribution of temperature in the cold and warm areas 

 respectively ; and in Fig. 57, the results ■ of the serial 

 soundings Nos. 52, 64, and 87, are reduced to curves. 

 Prom these diagrams, taken together, it will be seen 

 that in the first 50 fathoms there is a rapid fall of 

 nearly 3° C. Station No. 64 is a good deal farther 

 north than the other two, and the surface tempera- 

 ture is lower, so that the fall, which is nearly to the 

 same amount, starts from a lower point. The surface 

 temperature is doubtless due to the direct heat of 

 the sun, and the first rapid fall is due to the rapid 

 decrease of this direct effect. From 50 to 200 fathoms 

 the temperature in all three cases falls but little, re- 

 maining considerably above the normal temperature 



