26 THE OCEAN WORLD. 



One or two points worthy of notice may be recorded here. Shallow 

 water, and water near the coast, or covering raised sand-hanks, is colder 

 than water in the open sea. Alexander von Humholdt explains this 

 phenomenon by supposing that deep waters of higher temperature 

 reascend from the lowest depths and mingle with the upper heels. 

 Fogs are frequently formed over sand-banks, because the cold water 

 which covers them produces a local precipitation of atmospheric vapour. 

 The contour of these fogs are perfectly denned when seen from a 

 distance: they reproduce the form and accidents due to the sub- 

 marine soil. Moreover, we often see clouds arrested over these points, 

 which look from afar like the peaks of mountains. 



