AGASSIZ: THE FLORIDA ELEVATED EEEF. 37 



peculiar knife-edge layers, running at all angles, so striking in such 

 formations. 



Mr. Griswold also suggests that oolitic rocks are formed in the bottom 

 of the sounds. The oolitic sand and fragments of oolitic rock covering 

 the bottom of the Florida sounds is derived from the disintegration of 

 the aeolian rock and of the reef rock which constitute the substratum 

 and the highest parts of the keys, and from their extension inland 

 (perhaps twenty to thirty miles) along the southern extremity of 

 Florida from New River to Cape Sable. This whole territory being, 

 according to the determinations of Dr. E. 0. Hovey, based upon an 

 examination of the samples from the Key West Artesian well, underlain 

 at a depth of about fifty feet, or less inland, by Pliocene rocks and at a 

 depth of 700 feet by Eocene strata. 



Professor L. Agassiz, in his Report on the Florida reefs, 1 mentions the 

 existence of coral reefs in the interior of the mainland at a distance of 

 about five miles from the mouth of the Miami River. Owing to the 

 conclusions which he drew from the existence of this reef regarding the 

 probable mode of formation of a great part of the southern extremity 

 of Florida, his premises regarding the reef have been questioned. Pro- 

 fessor Shaler has described in detail a portion of the elevated reef 

 which he found at some distance from the shore line. This leaves no 

 doubt of the existence of an elevated coral reef of very great width, 

 or of a succession of patches and fiats covered by corals. The con- 

 clusions drawn from the presence of this elevated reef by Professor 

 Agassiz regarding the structure of the greater part of the peninsula of 

 Florida are thus seen to apply, though in a very modified sense, to a 

 comparatively narrow strip only of its southern extremity. Undoubtedly 

 some of the rotten honeycombed and pitted rocks which are observed 

 all along the shore of the mainland from Cocoanut Grove to the mouth 

 of the Miami River are composed of aeolian rock, the rock on the 

 shore line being the remnant of an extended series of low aeolian hills 

 of which the traces can be found here and there in the stretch of shore 

 mentioned. In one locality a bluff of aeolian rock fully twelve feet high 

 (Plate XIX.) is still standing, and testifies to the existence of an ex- 

 tended beach of coral sand derived from the wide stretches of now 

 elevated coral reef which undoubtedly flanked at one time the southern 

 shore line of the peninsula of Florida. Parts of this broad reef belt 

 are still visible to the southward as far as Bahia Honda and Sand Key, 

 and it can be traced uninterruptedly, except where covered by sand 



1 U. S. Coast Survey Report for 1851 ; Mem. Mus. Comp. ZooL, Vol. VII. No. 1. 



