301 [Shaler. 



eastern shore of that continent was to a great extent elevated during 

 the Pala3ozoic time. 



The fact that, although our knoAvledge of the geology of the south- 

 ern hemisphere is still very limited, two considerable areas of Tal- 

 ajozoic land have already been noticed, suggests the question 

 whether the southern half of the equatorial stream may not have 

 become broken before the close of the Palteozoic time. It may 

 be noticed that from the direction of the axis of elevation of these 

 two regions of Palaeozoic land, the resulting currents would have nec- 

 essarily been deflected southwardly, and thrown into the great south- 

 ern sea, and thus would have exercised no effect on the tempera- 

 ture or life of the northern hemisphere. Although there exists some 

 doubt as to the condition of the southern half of the equatorial 

 current at the close of the first great division of the geological action, 

 there can be no question that at the close of the Mesozoic time it had 

 become broken, certainly at one point, by the continent of South 

 America, and most likely by the elevation of a portion of the conti- 

 nent of Africa, so that since the beginning of the Tertiary period, life 

 in the southern hemisphere has been subjected to the influences of the 

 meridional system of currents. It will be an interesting problem for 

 the labors of the geologists of the southern hemisphere to ascertain 

 the relations of the organic life of the three continents during the 

 Mesozoic and Cenozoic times, and how far their features indicate the 

 separation into distinct oceanic basins at an early time. 



At the time when the southern portion of the equatorial current 

 had doubtless lost its original character, and become broken into 

 three meridional streams, it seems likely that the northern half of the 

 current still encircled the earth, probably much reduced in force by 

 friction along shores and shoals, but still retaining the essential features 

 of the intertropical movement, and effecting similar results. The 

 probability of this will appear when we consider those regions charac- 

 terized by Tertiary beds, and which we are justified in concluding 

 were submerged at the beginning of the present age. 



The greater part of the Peninsulas of Arabia, Hlndostan, and 

 Siam, were doubtless beneath the sea during the Eocene period ; the 

 absence of these extensive land areas Avould admit of the existence 

 of the trade winds over the Indian Ocean, and the unimpaired condi- 

 tion of the northern half of the tropical current, which since the eleva- 

 tion of those regions has not had any well marked character. 



Enough is knoAvn of the geology of Northern Africa to warrant the 

 supposition that it was submerged until nearly the present day. If 

 such was the character of the sea surfaces of this portion of the globe, 

 it is certain that a portion of the current of the Indian Ocean could 

 have poured through the sea of Southern Europe and Northern Africa, 



