392 J.D. Dana ona supposed change of Ocean Temperature. 
s se now, that by a change of level, America were to ter- 
minate in latitude 34° S., and Africa in latitude 56° S.: the rela- 
tion of the two, and of the cold influences of the currents adjoin- 
ing, would be entirely changed. The vast area in the South Pa- 
cific, embraced between the west South American coast and the 
isocryme of 74°,—which marks the influence in the colder season 
of the cold southern waters, though not by any means its extreme 
limit,—would, if transferred to the Atlantic equatorial regions, 
stretch nearly or quite across from Guinea to the East Cape of 
South America; and the line of 68° would sweep around north 
of the equator quite to mid-ocean. The actual extent of the 
change may be perceived with close accuracy if we transfer the 
isocrymal lines off this part of Western America to the Atlantic. 
In the Pacific, under the same circumstances, the line of 68° 
would nowhere reach within several degrees of the equator. 
The distribution of marine life would be greatly changed. 
While now the west coast.of South America is, as regards the 
ocean, one of the coldest regions for the latitude in the world, it 
would become very much moderated, and a considerable portion 
of coast would be bordered by tropical waters. Along by Lima, 
and far south, there might be coral reefs. In the Atlantic, on the 
contrary, the Gulf of Guinea now characterized by torrid waters, 
would be filled with the colder seas of the temperate zone, and 
true tropical life would be altogether excluded. 
e influence also on the Gulf Stream would be very decided 
and the whole North Atlantic would feel the change. 
It is a remarkable fact that while the west coast of America is 
bordered in the tropical part by cold waters, 10° to 12° below the 
mean of mid-ocean, and the marine zoology is hence extratropical, 
the temperature of the land is peculiarly torrid over the same lati- 
tudes. It is evident that in judging of the influence of the ocean 
temperature on the temperature of the land, the direction of the 
aerial currents for the year, should be considered as a most import- 
ant element towards any just conclusions. 
Although we cannot show that the supposed change of level in 
the continents has taken place, we may learn from the facts what 
vast changes in marine life, have happened in past ages, through 
such changes of level as have occurred in the earth’s history. 
The changes on the land from this cause would be less marked ; 
besides, these have had far less influence on the life of ‘the rocks 
than those of the ocean, as the fossiliferous rocks are mainly 
of marine origin. We know that in the cretaceous and tertiary. 
_ periods, the Andes were in part under water, or at a much lowet 
level, and effects of the kind considered, cannot be altogether 
hypothetical. 
