642 Proceedings of the Royal Society 
/ 
at the same depth, at temperatures differing often by many de- 
grees. 
Viewing these temperature observations with the indications given 
by the soundings, we arrived at the generalisation — that contiguous 
areas with widely different bottom temperatures were separated by 
submarine barriers, and that the depth at which the minimum 
temperature was found in one of the areas , indicated the height of the 
harrier. 
The following diagram (fig. 1) will illustrate: — 
The water which is cooled down in the Polar seas, and has thus 
acquired a high specific gravity, flows along the bottom into the 
deepest part of the ocean to which it can find access, as shown by 
the arrows. The surface of the earth below, as well as above the 
level of the sea is irregular, and the result of this irregularity is that 
masses of water meet with barriers, over which they must pass, like 
that represented in the diagram (A). 
A barrier like this surrounding a depression, cuts off the lower and 
colder layers of water, and the basin beyond is filled with water at 
a uniform temperature by an overflow, the temperature being the 
same as the water at the height of the ridge, as shown in the 
diagram. 
In any region, then, where we have different bottom temperatures 
in contiguous areas, and where the minimum temperature in one of 
the areas is reached at some distance above the bottom, we thought 
we had reason to believe that the point at which the minimum 
temperature is found indicates the height of the submarine ridge 
which cuts off the underflow. 
This generalisation induced Captain Tizard to predict the existence 
