328 On (he Geological Arrangement of Ancient Strata. 



titudes, and at different depths, are still wanting. We give the follow- 

 ing results : 



Lat. Temp, of Surface. Depth, 



3° 26' S. 73'' 1000 fath. 



20''30'N. 83" 1000 ... 



9°2rN. 83' 250 ... 



OEquat. 83" 300 ... 



Mean reduction of temperature in Tropics, 

 Lat. Temp, of Surface. Depth. 



36° 9'N. 7r9 100 



30° 39' S. 67 300 



44° 17' S. 54°9 196 



Mean reduction of temperature in Temperate Zone, 1° in 28 fathoms. 



It thus appears that, within the range of the tropical and temperate 

 zones, there is a decrease of the temperature from the surface down- 

 wards of one degree in every 25 to 28 fathoms. In colder regions, when 

 the temperature is at or below 38°, the cold surface water, being heavier, 

 sinks, while a warmer stratum rises from below to supply its place.* 



Peron found the temperature of the ocean to decrease gradually from 

 the surface downwards, and Ellis found it stationary at the depth of a 

 mile. 



On the whole, then, it may be assumed as a general rule, that, in tro- 

 pical and temperate regions, the ocean decreases in temperature from 

 the surface downwards, that this decrease is greatest in the upper por- 

 tions, while, at certain depths, the temperature may remain almost sta- 

 tionary. In temperate and tropical latitudes the shallowest parts of the 

 ocean are the warmest ; in this way, the waters of estuaries and long 

 ranges of littoral shallow seas will be of higher temperature than the 

 deeper portions, or even than shallow reefs far out at sea. Inland seas, 

 where there are no tides, will also vary in temperature according to 

 latitude ; in low latitudes, such seas as the Baltic will be colder than the 

 ocean. It will thus appear that the ocean, like the atmosphere, has its 

 zones of temperature, but in the reverse order, the upper portions of 

 the waters of the ocean being warmest ; while those next the earth are 

 of a lower temperature. The upper zones of the ocean are full of life, 

 both vegetable and animal ; but, like the atmosphere, there is a limit, 

 beyond which, neither plants nor animals will be found. This limit is 

 caused not alone by diminished temperature, but also by diminished 

 light, and probably by other causes, such as increased density, and the 

 deficiency of atmospheric air and influence. We do not, as yet, exactly 

 know the depth at which marine plants and animals totally disappear ; 

 but the fact is established beyond all doubt, as soundings made in deep 

 water, and at considerable distances from the shore, bring up mud or 

 comminuted rocks, but no traces of organic beings. It is probable that 

 this depth varies according to latitude. 



* Scoresby, Ross. 



