36 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



reef north of Fowey Rocks, to the disconnected patches west of Alli- 

 gator Reef as far as Sand Key, and to the open line of keys stretching 

 west of Key West to the Marquesas. 



The outer reefs are growing upon old reef rock ledges, now elevated. 

 They flourish on the ruins of the old reef, which itself must be under- 

 lain by the shore extension of the formation known as the Pourtales 

 Plateau. This near the outer edge of the reef is covered with sand 

 and reef material, so that its ill-shore limit cannot be determined except 

 by borings. According to Mr. Hovey's determination, the thickness of 

 the elevated reef at Key West is probably not greater than fifty feet. 



It now becomes an interesting question to trace on the mainland the 

 inuer limits of the elevated reef. What we know of the subject we owe 

 to the observations of Professor L. Agassiz and Professor Shaler, but 

 they only penetrated a comparatively short distance inland from the 

 shore of Key Biscayne. To obtain additional information on this point, 

 Mr. L. S. Griswold made, at my request, an expedition into the interior, 

 with the intention of reaching Long Key on the edge of the Everglades, 

 and of ascertaining the nature of the rock which is said to crop to the 

 surface at that part of the Everglades. 



Mr. Griswold succeeded in reaching a point close to the so called 

 Long Key, 1 and gives a most interesting account of the appearance of the 

 southern part of the Everglades. He penetrated inland a distance of 

 about twenty-three miles. He ran three lines into the interior, one from 

 Black Point Creek, at the western extremity of Key Biscayne Bay, a 

 second line following the Miami River and branching off in a westerly 

 direction towards Long Key, and a third line following the course of 

 New River. He also explored Florida Bay as far as Cape Sable to the 

 east, and extended his observations to the north along the east coast of 

 Florida, examining such localities as Boca Ratones, Lake Worth, Linton, 

 and Cape Canaveral. 



Mr. (iris wold traced the extension of the aeolian limestones more or 

 less modified to the most distant point he reached, though he consid- 

 ers the oolitic rocks he collected as having been formed under water, 

 an opinion with which I cannot agree. The specimens he has col- 

 lected are all, in my opinion, only modified ceolian rocks, such as are 

 found anywhere in the Bahamas and Bermudas. The very oolitic bluff 

 to the westward of Miami River, — a photograph of which I owe to him 

 (Plate XIX.), — which in his opinion has been deposited in water, is 

 a most characteristic ajolian rock, showing in its stratification tnc 



i See his route, Plate XVII. 



