158 SATURDAY LECTURES. 



west from Florida. Formerly it was sif^posecl that the 

 peninsula of Florida was due to alluvium from the rivers 

 of the Mississippi valley and other sources settling against 

 a barrier of coral reefs which grew toward the south and 

 west, as their northern portions were smothered by sediment. 

 This shows, however, that the coral reefs have simply availed 

 themselves of the advantages presented by the steep edge of 

 the above-mentioned plateau so abundantly supplied with 

 iood for them by ocean currents; and that, in its main 

 features, Florida was outlined hj different and far older 

 agencies than the now existing coral reefs. The same is 

 evidently true of Yucatan. 



•To another point I would call your attention as of econ- 

 omic interest. We know that by most engineers it is be- 

 lieved that experience has proved that channel-making by 

 the jetty process is a mere temporary alleviation of bars and 

 other obstructions to commerce. The j)ermanent success of 

 the Eads' jetties is even now a matter of doubt, and there is 

 no doubt that in time extensions will be called for. But it 

 w411 be observed that at no other point on the Gulf coast of 

 the United States is the 100 fathom line so near the actual 

 coast as here, and the inference is, perhaps, not too far 

 fetched that, therefore, not only is it probable that with 

 certain extensions of the jetties (other circumstances per- 

 mitting) a point will eventually be reached where the slope 

 seaward is so steep that a bar can hardly form or be main- 

 tained, but also that at no other point on the whole Gulf 

 coast could the jetty system have been applied to the im- 

 provement of a river mouth with any reasonable prospect 

 of maintaining a permanent channel. 



It may also be observed, from an examination of this 

 model, what we should find confirmed by an equally thorough 

 survey of the ocean at large, (as Ave know from recent exam- 

 inations of the Atlantic sea-bed,) namely, that while the 

 sea-bed, like the dry land, has its irregularities, the}' differ 

 in character from the irregularities of the dry land. It is 

 true that sharp peaks and elevated rocky areas have been 

 discovered in both the Atlantic and Pacific, though none 



