232 CARNEGIE INSTITUTION OF WASHINGTON. 



rim after its formation had been elevated about 50 feet and then depressed. 

 The presence of submerged overhanging cliffs was mentioned and it was stated 

 that the work of subaerial agents should be considered. Studies of the 

 bank around Loggerhead Key showed the bottom to be composed of rock, 

 which is frequently bedded, and whose surface is pitted, jagged, caver- 

 nated, and tunneled, with a zone of undercutting the upper edge of which 

 ranges in depth from 16 to 24 feet. As the pits, cavernations, and tunnels 

 resemble those observed, but not carefully studied, on subaerial limestone 

 surfaces, and as the overhanging submerged cliffs suggested that they are 

 cliffs wave-cut at the base and subaerially sculptured on the top, a detailed 

 study of the minor sculpture of the limestone surfaces, both above and within 

 the reach of the waves, was undertaken in the Bahamas, and a considerable 

 body of information, with accompanying photographic illustrations, was 

 accumulated. It was not practicable to reexamine the bottom of theTortugas 

 area with requisite thoroughness to be positive in expressing an opinion as to 

 the origin of the submerged sculpture in that area, but pre\dous observations 

 combined with additional somewhat casual observations strongly suggest 

 submerged surfaces which were sculptured at or above the upper reach of 

 waves, while wave-cut cliffs occur at lower levels. 



This line of investigation appears to be of a high degree of importance 

 because of the possible assistance it may render in the interpretation of the 

 geologic history of flat-lying limestone areas. The significance of indented 

 shore-lines and submerged valleys has long been recognized and deductions 

 from them are possible where there are land masses which are of appreciable 

 relief and which are largely composed of non-calcareous material. Calcareous 

 deposits of low relief do not develop conspicuous drainage systems, as the 

 waters form underground tunnels and runways and thus sink below the 

 surface. Therefore, in such areas as southern Florida and most oceanic 

 atolls, as the investigator is deprived of the aid of gross physiographic features 

 in interpreting geologic history, he must seek other criteria, and it appears 

 that needed assistance may be found in the study of the minor sculpture 

 of limestone surfaces and in the application of principles deduced therefrom. 



FLORIDA. 



The investigation of the bottom deposits of Florida along the reef-tract 

 was continued during June 1914, and samples were collected from a number of 

 additional stations between Cape Florida and Tortugas. Portions of the 

 samples have been sent to Dr. Cameron for physical analyses and to Dr. 

 Mann for a report on the diatoms. Bottom muds and water samples for bac- 

 terial study were sent Dr. Kellerman from Featherbed Bank, Biscayne Bay, 

 from a mud fiat about 2 miles north of Key West, and from Marquesas lagoon; 

 notes on his results are given on pp. 228, 229. 



The study of the shore-line physiography of southern Florida and of the 

 agents shaping and building banks was continued, and certain studies, espe- 

 cially those of currents, were made in some detail. 



Some attention was paid to the valley profile and the character of the 

 channel of Miami River at Miami. There is along the stream a low terrace, 

 cut into the Miami oolite, to a level about 10 feet below the general level of 

 the Miami oolite plain. The stream has trenched its channel to a depth of 

 about 9 feet below sea-level. The lower terrace extends to the shore of Bis- 

 cayne Bay and connects with a low, fiat terrace lying between the bay and a 

 slightly elevated wave-cut escarpment which runs from Devil's Punchbowl 

 southward through Cocoanut Grove to an undetermined distance beyond. 

 The seaward face of the keys was inspected from Soldier's Key to Knight's 

 Key. 



