140 REPORTS OF INVESTIGATIONS AND PROJECTS. 



Geology of the Keys, the Marine Bottom Deposits, and Recent Corals of 

 Southern Florida, by T. Wayland Vaughan, U. S. Geological Survey. 



Boca Grande Key. — Beach ridges of calcareous sand occur on the west, 

 south, and east sides of this key ; behind them are mangroves in the swampy 

 areas and bordering the tidal creeks. Over a considerable area of the in- 

 terior, however, oolite outcrops. This is the most westerly locality from 

 which this rock is at present known. 



The Marquesas. — This group forms an atoll, with an interior lagoon, sea- 

 wardly bounded by an interrupted ridge of calcareous sand rising a few feet 

 above the ocean's level. No hard rock of any kind was observed on them. 



The Tortugas. — Sand, Middle, and East keys were examined and found 

 to be composed of calcareous sand. Long Key is mostly made up of wave- 

 tossed stems of Acropora and molluscan and echinoid tests. Bush Key, 

 which is covered at high tide, has wave-tossed coral blocks on its summit, 

 and the sea-bottom around it is covered with similar material. 



A report on the bottom samples collected during April, 1908, has been pre- 

 pared for publication and will appear in the next volume of reports from 

 the Tortugas Marine Biological Laboratory. 



STUDIES ON MADREPORARIA. 



Survey of the Coral Fields. 



Additional observations were made on the local conditions under which 

 the various species of corals occurring around the Tortugas live, and the 

 mapping of the fauna with reference to all ascertainable factors was con- 

 tinued. As yet the various collections have not been critically studied in the 

 laboratory, but in the field it is shown that each species occurs under a more 

 or less definite set of conditions, and in the Tortugas area there are three or 

 four coral faunal complexes, the species of one complex only slightly over- 

 lapping those of another. The careful survey of the region is not complete. 



Annual surveys of the piers of the Fort Jefferson dock. — Numerous species 

 of corals grow on the piers of the Fort Jefferson dock, which faces the deep 

 channel on the east side of Garden Key. The maximum depth of this channel 

 is 6 fathoms and the tidal currents flow gently through it. The species of 

 corals vary with reference to the position of the piers, and it was thought 

 careful records of the species growing on each pier would give results show- 

 ing the influence of several factors in determining the habitat of the respec- 

 tive species. These surveys also afiford material for growth observations. 

 They were begun in 1908, and continued in 1909. 



Annual surveys of the Fort Jeiferson moat. — The sea has access to the 

 moat surrounding Fort Jefferson, and a number of species of corals grow in 

 it. The movement of the water in it is sluggish, and during periods of heavy 

 rain its degree of salinity is less than that of the ocean. The general vital 

 conditions prevalent in the moat simulate those of a flat inside a key except 

 it is subject to greater variation in the degree of salinity of the water and 

 because of deficient circulation the water may become more highly heated by 

 the sun. The corals are not uniformly distributed in the moat. Therefore 

 in 1908 a detailed survey of it was made to determine the distribution of 

 each species living in it and to see if factors determining the habitat could 

 be discovered. Numerous growth observations are being conducted on the 

 species living there. Transplanting experiments in it are described subse- 

 quently. The surveys are being repeated annually to note any changes. 



