154 REPORTS ON INVESTIGATIONS AND PROJECTS. 



M IF! IS I': 



interrupted ridges or hills from 30 to 100 feet high. The rock at Driggs 

 Hill, near Sharp Rock Point, is composed of oolite entirely to its summit, but 

 the exposures examined were inadequate for forming a conclusion as to 

 whether or no the rock is an eolian accumulation. Although the origin of 

 the rock composing the ridges is in doubt, it can be positively stated that the 

 rock underlying the general low-land, above which they stand, is a marine 

 oolite, similar in all respects to that so abundant in southern Florida. This 

 oolite extends through South Bight from the east to the west coast, and con- 

 tains Pleistocene marine fossils at many localities. The bottom samples 

 show that oolite forms the sea floor across the Great Bahama Bank through- 

 out the entire distance between Gun Cay and Northwest Passage. 



Both Gun and North Cat cays are largely composed of indurated, wave- 

 tossed, detrital, calcareous sand, under which is an oolitic foundation. 



It is evident that there are in the Bahamas three classes of material, viz, 

 (1) extensive areas of marine oolite which form the great platform of An- 

 dros Island (or the Andros group of islands) and probably the platform of 

 New Providence Island; (2) ridges and heaps of wind-blown calcareous 

 material, Nassau Ridge being an instance of this kind of deposit; (3) wave- 

 tossed and perhaps wind-shifted detrital material. More detailed investiga- 

 tions are needed to ascertain the extent of the areas underlain by each of 

 these classes of deposits. 



Several kinds of evidence bearing on oscillation were obtained on Andros 

 Island. The marine fossils occurring at many localities above sea-level fur- 

 nish proof of elevation. One of these localities, Sharp Rock Point (see map 

 of Golding Cay entrance), will be specifically mentioned. This point, at 

 northeast corner of South Andros Island, is composed of marine oolite. A 

 short distance within it, between the "White House" shown on the map and 

 the point of Sharp Rock Point, fossil corals, mostly Mceandra strigosa, 

 occur embedded in the oolite, at an elevation of 5 or 6 feet above mean 

 water-level. As many of the specimens appear to be in their natural grow- 

 ing position they indicate a slight elevation. Evidence of depression is 

 afforded by submerged pot-holes. The present land surface of the oolite is 

 rough, frequently almost devoid of soil except in pot-holes, locally known as 

 "banana holes," because of the conditions they offer for the growing of 

 banana plants. The depth of such pits may be as much as 10 feet. Sub- 

 marine holes, known as "blue holes," are numerous in the vicinity of the 

 eastern mouth of South Bight. Six of them, five off the eastern shore of 

 Mangrove Cay, were examined in detail. Their depth ranges from 13 to 36 

 feet, while that of the surrounding water is 7 feet or less ; their diameter may 

 be as much as 200 feet, but is usually less, probably 20 to 40 feet. The 

 largest hole examined, Blue Hole, north of Bastian Point (see map of Gold- 

 ing Cay entrance), has a diameter of about 200 feet and a maximum depth 

 of 21 feet. These holes are undoubtedly submerged pot-holes and indicate a 

 depression of at least 36 feet. Criteria are at present lacking for the positive 

 determination of whether the last oscillation was upward or downward. It 

 seems probable, however, that there was an elevation of perhaps 60 feet 

 after the formation of the oolite platform, and that subsequently there has 

 been a depression of at least 36 feet, but not sufficient to bring the marine 

 deposits again below sea-level. 



The geologic data collected, although fragmentary, are important, and will 

 be of great value in making detailed plans for future investigations. 



An attempt was made to dredge off the eastern shore of the north end of 

 South Andros Island, opposite Sharp Rock Point, partly to obtain corals and 



