400 T. C. CHAM BERLIN 



side, this loop of the Greater Gulf Stream gives off a branch into 

 the Mediterranean Basin, and that out of this branch of the Gulf 

 Stream group there arises later by evaporation the lower Mediter- 

 ranean stratum, which in turn forms part of the middle layer of the 

 Atlantic waters. This I shall emphasize later. The point is that 

 here is a declared case of the passage of the upper layer consisting 

 of one type of waters into a middle layer of another type of waters, 

 and this middle layer later plays an essential part in the explanation 

 of polar ameliorations here offered, and in later applications of a 

 more general nature. 



The main branch of the Greater Gulf Stream flows onward to 

 the northeast, and greatly affects the climate of northwestern 

 Europe, as is well known. A large portion of the Gulf Stream 

 passes over the Southern Intercontinental Ridge, and in the tract 

 between the two intercontinental ridges is much modified by branch- 

 ings, interdigitations, whirls, and various irregularities. Passing 

 on over the Northern Intercontinental Ridge, this much modified 

 stream, as here interpreted, forms the main source of the upper 

 layer of the Polar Sea described above. We will return to this last 

 point in connection with the middle Atlantic layer. 



All this group of currents, here called for convenience the Greater 

 Gulf Stream, are surficial, warm, and rather low in salinity, except 

 as their salinity is increased by interchanges and interdigitations 

 with waters of the adjoining saline layers. 



h) The cold currents of the polar outflow. — Over against these 

 warm, surficial waters flowing poleward, stand a group of cold polar 

 currents flowing southward. Their primary source is in the ice- 

 field of the surface layer of the Polar Basin. These are gathered 

 into the Labrador current as their main trunk stream at the south. 

 These occupy the surficial position of the Atlantic column on its 

 west side, corresponding in that respect to the Greater Gulf Stream 

 on the east side. The two may be regarded as the complements of 

 each other. The cHmatic function of the one is to carry heat north- 

 ward; that of the other is to carry cold southward. But this is 

 done at great loss, for both are surficial. Moreover, their waters, 

 instead of being altogether the same throughout their journeys, are 

 constantly changing by intermixture with other waters as a part of 



