GEOLOGY. 311 



the coral a foothold and not have raised the recently formed land. The rising 

 by sedimentary deposit, on the other hand, can affect nothing but the sea-bot- 

 tom, and to this cause the speaker referred that uprising which forms the 

 necessary condition of the horizontal extension of the coral reefs. 



Xow to proofs that such deposits have actually taken place : It is a law of 

 currents that if their velocity is checked they deposit a portion of their sedi- 

 ments upon the bottom ; if it is increased, they wear away their beds and 

 banks. If the velocity of the stream be greater on one side than on the other, 

 they abrade one bank and deposit the abraded matter on the other. Such a 

 current, in making a curve, necessarily has a greater velocity on the outside 

 than on the inner; the outer bank will then be abraded, and a tongue of land 

 be formed on the other side. If instead of the tongue of land you have a body 

 of still water around which the current sweeps, deposition of sediment will 

 begin and go on until you h%ve the tongue again ; and this is necessarily true 

 under ah 1 circumstances. It is of no consequence whether the limits of the cur- 

 rent be solid banks or banks of still water. A sediment bearing stream making 

 a sweep or curve in still water must deposit its sediment principally upon the 

 inner side of the curve, thus forming shoal water. The curve will extend, 

 and the shoal in proportion. The Gulf Stream is such a current, making a 

 strong sweep around the point of Florida. The result of this reasoning is, that 

 the sweep of the curve of the Gulf Stream has been extending for ages, and the 

 peninsula has kept pace with it by means of sedimentary deposit. Or suppose 

 Florida was once represented by a shoal of the same form and extent, this 

 shoal must become constantly shallower from the same cause. If, then, the 

 Gulf Stream carries sediment, the above conclusions must follow. This stream 

 is supposed to be a continuation of the great Equatorial current crossing the 

 Atlantic, dividing at Cape St. Roque, the northern branch uniting with the 

 waters of the Amazon and Orinoco running along the coast of South America, 

 through the Caribbean Sea into the Gulf of Mexico, emerging between Florida 

 and Cuba, and running off to the north. This stream we know carries the 

 sediment of the Amazon and Orinoco in a visible form for several hundred miles. 

 Much of this is no doubt deposited along the South American coast, but 

 according to Humboldt much is carried into the Gulf. Into the Gulf is also 

 poured the vast amount of sediment of the great Central Xorth American 

 Rivers, especially of the Mississippi, and those turbid waters form the Gulf 

 Stream ; for Lyell has proved that all these currents and streams mingle their 

 waters in this great basin. It was here shown that all this sediment could 

 not be deposited in the Gulf itself, by calculations based upon the depth 

 and velocity of the stream and the distance (500 miles) from the mouth 

 of the Mississippi to the Tortugas. It was also shown that such a sinking of 

 the sediment from the surface would take place that the Stream would have 

 a clear and transparent stratum of water at the top of some 60 and 70 feet in 

 depth, at the close of the seven days required for it to pass from the mouth of 

 the Mississippi to the point of Florida. In this respect the Gulf Stream, flow- 

 ing between the banks of still water, differs from a river broken by a rough 

 bottom and impinging upon irregular sides. The lower strata of the Stream 

 may then be filled with sediment, though the upper be clear. One other fact 



