GEOLOGICAL SOCIETY OF MANCHESTER. 



185 



From these observations it is evident, that, at a depth 

 comparatively small, there exists a very large portion of water 

 having a temperature of about 40*^ Farenheit, at which tem- 

 perature water is more dense than at any other. 



The mean depth of the Pacific Ocean is supposed to be 

 about four miles, and the Atlantic about three ; the mean of 

 which would make the depth of the ocean about 3000 fathoms, 

 in round numbers. At the depth of about 800 fathoms, there 

 is every reason to believe that the temperature of the sea is 

 about 40° Farenheit; and also, that the remaining 2,200 

 fathoms is of the same heat, may be inferred from its then 

 being at its greatest density ; for, if the water at a greater 

 depth w^ere either colder or hotter, then it would ascend in 

 consequence of its being specifically lighter. 



If this inference of the great density of so large a portion 

 be correct, it necessarily follows, than any alteration in its 

 temperature must cause a corresponding alteration in the 

 mean sea level. By a decrease in heat, an increase in depth 

 would be the consequent result. 



Water, according to Dalton, in assuming a solid state, 

 increases 0"05 in volume ; so that, were all the waters of the 

 ocean to be converted into ice, there would be a great increase 

 in volume ; the depth being dependent entirely on the area of 

 surface. 



Although the supposition of the ocean having been con- 

 verted into ice be entirely gratuitous, yet it in no way affects 

 the conclusion, that a decrease in temperature would cause a 

 corresponding increase in the volume of the waters of the 

 ocean. It is while in the act of freezing that waters expand 

 0*05 ; so that, during the time of cooling from the tempera- 

 ture of its greatest density, a gradual increase in volume 

 would follow. 



The former occurrence of the sea above its present level 

 does not depend merely on the supposed former existence of 



