310 ANNUAL OF SCIENTIFIC DISCOVERY. 



elevated by igneous agency, is found to be an error when excavations are 

 made, as they are then revealed to be but boulders. The conclusion from 

 this reasoning follows inevitably that the line of keys is a former coral reef 

 changed by the action of the waves as above described. In this manner, as 

 Tuorney pointed out and Agassiz has proved, was the present Southern coast 

 formed. Here also Tuomey supposed he saw evidence of upheaval, while 

 Agassiz saw nothing but the effect of the waves. The line of the shore was once 

 a reef, then became keys, finally a continuous coast line, behind which the shoal 

 water rapidly filled up, and the Everglades were formed. Of course, during 

 the reef period, the elevated line from Chatham Bay was the coast. The 

 coast also must have been begun as a coral reef, which went through the 

 same changes, at a time when the line from Tampa Bay was still the limit 

 of the peninsula. It is clear that all this portion of southern Florida was 

 superficially formed by coral agency ; and we can hardly doubt that this is 

 equally true of the country much further to the northward, for specimens of 

 precisely the same coral have been collected as far north as St. Augustine. 

 This opinion Mr. Le Conte fortified by various other facts and arguments. 

 Thus far we have Prof. Agassiz's views upon the mode of formation of this 

 region. That the coral agency, however, was not alone sufficient, the speaker 

 now proceeded to show : 



First : It is a well known fact that the reef-building corals of those seas 

 cannot grow at a greater depth than sixty to seventy feet ; nor can they 

 grow above the surface of the water at low tide being thus confined verti- 

 cally to limits of ten or twelve fathoms. Unless there be a subsidence of the 

 sea-bottom, therefore, we can have no reef of greater extent than this ; in case 

 of coral islands, we may add ten or fifteen feet for materials thrown up by 

 the waves, which, where there is no subsidence, limits the extremes to some 

 eighty feet. 



Second : It is certain that no subsidence of the sea-bottom has here taken 

 place, as that would preclude all possibility of the increase of the peninsula 

 by coral agency. It follows then that the coral formation of Florida can be 

 nowhere beyond eighty feet in thickness. Now if coral agency alone is to be 

 admitted, it follows that the ocean, for the enormous distance from St. Augus- 

 tine to the present reef, was nowhere above sixty or seventy feet in depth ; 

 and Florida was originally represented by a tongue-formed shoal three hundred 

 miles in length ! Suppose this to have been the case, why did not the corals 

 grow over the whole extent, and form a coral field, instead of appearing in a 

 succession of reefs ? This proved conclusively to the speaker that the condi- 

 tions of coral growth were progressively more and more southwardly. The 

 facts in the case prove that the sea-bottom has been gradually rising from 

 north towards the south. 



TJdrd: The gradual rising of the sea-bottom may be occasioned either by 

 igneous agency or by sedimentary deposit. Prof. Tuomey supposed that he 

 had found evidences of the former, but Agassiz has satisfactorily explained 

 those appearances on which the deception was based, and we may with full 

 confidence say that there is no evidence of any such igneous action. It is 

 inconceivable that a sufficient elevation could have taken place to have afforded 



