Shaler.l 300 



past history of ocean streams. If continental areas have been per- 

 manently submerged and converted into the floors of deep seas, we may 

 thereby have lost all trace of agents capable of producing currents 

 which ceased to exist with the disappearance of the cause. If, how- 

 ever, we accept the existing continents as the only great folds of the 

 earth's crust which have ever existed, and admit that when the upfold 

 of the continental elevations, and the downfold of the sea beds had 

 begun, all further corrugation of the crust would result in the devel- 

 opment of these features, we have some ground on which to base con- 

 clusions as to the geography of past periods. 



Although the existing state of our knowledge of the outline of the 

 land at successive geological periods does not admit of any very trust- 

 worthy conclusions as to the past history of ocean currents, we may 

 still trace some of the changes of the equatorial current in certain 

 conditions of the sea area likely to have existed as the continents were 

 developed. 



It is eminently probable that no portion of the continent of North 

 America, of sufficient size to exercise any effect on oceanic streams, 

 existed in intertropical regions anterior to the close of the Carbonifer- 

 ous period. It is equally probable that that portion of South America 

 lying to the north of the Equator was also beneath the sea during 

 the Palaeozoic time. Therefore we are justified in the conclusion that 

 up to this stage in the earth's history the northern sec^tion of the equa- 

 torial current had not been interrupted by the American pair of Con- 

 tinents. The little that is known of the geology of Northern Africa 

 leads us to suppose that this continent could not have had that por- 

 tion of its mass north of the southern line of the Sahara brought 

 above the sea line until the Mesozoic time, if not later. The south- 

 ern portion of Asia, including Arabia, Ilindostan, and Siam, have 

 presented us with no evidence of Palaeozoic land. Thus it seems 

 probable that the first great series of changes which the land and 

 seas underwent did not destroy the northern half of the equa- 

 torial current. The condition of the southern half of the equatorial 

 current at the close of the Carboniferous period, is much more doubt- 

 ful. We have unquestionable evidences of the existence of a consid- 

 erable area of Carboniferous land in Southern Brazil, and it is quite 

 likely that the axis of elevation was prolonged northwardly, in the 

 eastern range of that empire, giving to the Southern Continent an 

 axis corresponding in age to the Appalachian chain. In Australia, we 

 have evidence of the existence of extensive land areas during the 

 Carboniferous period, and though it is not yet proven that they had a 

 northward extension sufficiently great to break the southern portion 

 of the stream, the direction of the axis renders it probable that the 



