DEPARTMENT OF MARINE BIOLOGY. 1 53 



(5) A study of chemically fertilized Cidaris eggs. 



(6) A study of the Cidaris female X Toxopnenstes male cross. 



(7) A study of the Cidaris female X Hipponoe male cross. 



Through the kindness of Prof. R. T. Jackson, I have also a series of prob- 

 able Hipponoe X Toxopneustcs adult hybrids for study. 



Studies of the Geology and of the Madreporaria of the Bahamas and of 

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



BAHAMA EXPEDITION. 



The expedition to the Bahamas left Biscayne Bay, Florida, under Dr. 

 Mayer's direction on April 28 and returned on May 27. The program for 

 my work comprised (i) a study of the geology of the localities visited and of 

 present geologic agencies in order to obtain a basis for the interpretation of 

 the geologic history of the region; (2) a study of the Andros Barrier Reef 

 and of the general ecology of the corals; (3) experimental investigations of 

 the growth-rate and of variation of corals. Because of continued high winds 

 the program could not be fulfilled in two particulars. It was not possible 

 to do the dredging needed to ascertain the lower bathymetric limits of the 

 shoal-water corals, and procure the collections necessary for a study of vari- 

 ation with increasing depth ; nor was it possible to establish a coral plantation 

 on the outer reef. In all other respects, however, the program was executed 

 as planned. 



Information on a number of subjects was gleaned in the field, considerable 

 collections of bottom samples, rock specimens, and corals were made, and a 

 large series of experiments and observations on the growth-rate and on the 

 effect of environment on the variation of corals was initiated at the eastern 

 end of South Bight, Andros Island. As this was a preliminary expedition 

 and as the collections made have not yet received detailed laboratory study, 

 it is at present possible to give only some general results. 



Special attention was paid to the geology of New Providence and Andros 

 islands, and North Cat and Gun cays were again examined. Although the 

 rock specimens collected have not been studied in the laboratory, some con- 

 clusions reached in the field may be stated. New Providence Island is com- 

 posed of a platform of oolitic limestone, similar to that found in southern 

 Florida. The height of the platform ranges from sea-level to an elevation 

 of about 20 feet. Rising above the "plains" are several ridges, the most im- 

 portant of which are the ridges south of the sea-front at Nassau and Blue 

 Hills, south of Grantstown Plain.* 



The height of Nassau Ridge is about 100 feet, while that of Blue Hills, 

 according to my aneroid, is about 75 feet. The ridge at Nassau is evidently 

 an eolian accumulation, as Mr. Agassiz has contended, but I doubt the eolian 

 origin of the rock underlying the platform on which the ridge stands. More 

 detailed information was obtained on Andros Island. 



Andros Island is in reality a large group of islands. The area south of 

 South Bight will be referred to as South Andros Island. These islands are 

 composed of an extensive platform, ranging in elevation from sea-level to 20 

 feet or perhaps slightly more. The eastern front is higher than the western. 

 Along the eastern side of South Andros Island and of Mangrove Cay are 



*A. Agassiz gives a detailed description of the physiography of New Providence 

 Island and a profile section in his "A reconnaissance of the Bahamas and of the ele- 

 vated reefs of Cuba." Bull. Mus. Comp. Zool., vol. 26, 1894, pp. 18-24. 



