ANTILLEAN-CARIBBEAN REGION 



883 



(4) Where examined, the outer rims of all the valleys rise steeply, perhaps 

 even as vertical cliffs, from a depth of about 500 fathoms (3,000 feet) to the 

 edge of the platform. 



(5) The Tongue of the Ocean and Exuma Sound Valleys are parallel, and 

 about 50 miles apart, but the Tongue of the Ocean slopes continuously north- 

 west from its shallowest point at a depth of about 720 fathoms (4,320 feet), 

 whereas Exuma Sound, starting from a similar depth, slopes continuously in 

 the opposite direction, southeast. 



(6) Where "tributaries" meet the "main stream" they appear to do so at the 

 same level or "at grade," and where the valleys enter the ocean basin proper, 

 they do so at the same level. 



Andros Island Deep Test. A deep test well was drilled on Andros 

 Island of the Bahamas to a depth of 14,585 feet, and enhances our knowl- 

 edge of this little-known region immensely. The following details were 

 given orally by Maria Spencer at the St. Louis meetings of the American 



Log of Andros Island Deep Test 



Depth, Feet 



Recent and Miocene (?) 









Limestone as at surface. Corals and 



bryozoans 



0-530 



Limestone, dolomitized 







530-1625 



Coquina 







1625-2200 



Eocene 









Coquina of microfossils 







2200-2640 



Alternating limestone and dolom 



ite 





2640-4640 



Paleocene (?) 









Dolomite, fine-grained 







4640-6220 



Dolomite and chalky limestone 







6630-7590 



Paleocene or Upper Cretaceous 









Dolomite, brown 







7990-8760 



Upper Cretaceous 









Dolomite, tan, granular 







8760-9760 



Dolomite, coarsely crystalline, cavernous 



9760-10,035 



Limestone, part brecciated, part 



cha 



Iky, cemented with 





brown dolomite 







10,036-10,660 



Cavernous 







10,660-10,709 



Dolomite, fine-grained 







10,709-11,940 



Limestone, creamy white, chalky 







11,940-12,480 



Lower Cretaceous 









Dolomite, crystalline and porous 









Sunnyland zone in Florida 







12,480-13,710 



Bottomed 







14,587 



Association of Petroleum Geologists, 1949, and taken down as notes by 

 the writer. 



Spencer commented that the Upper Cretaceous section has the same 

 thickness as that of Florida, but it consists of dolomite and limestone, 

 whereas the Florida section is nearly all limestone. The base of the Lower 

 Cretaceous was not reached in the Bahama test, but the 2100 feet known 

 consists mostly of crystalline dolomite, whereas the Florida section con- 

 sists of limestone, anhydrite, and dolomite. 



Reef Building. Heretofore it could be said only that reef limestones ait 

 prominent in many places on the Bahama Islands and have been studied 

 below sea level. A bore hole 395 feet deep on New Providence Island 

 passed through Pleistocene and into Miocene reef material (Hess, 1933 ). 

 The calcareous material consisted mostly of calcite to a depth of 165 feet, 

 and below it was mostly dolomite. The porosity decreased to 5 percent at 

 the bottom of the hole. Hess recognizes nearly everywhere almost clifflike 

 dropoffs of the submarine canyon walls, ridges, and platforms, from the 

 surface down to a depth of 4000 feet, and believes this feature could not 

 be accounted for by erosion, but on the contrary to reef upbuilding. He 

 finds no geophysical evidence to dispute a conclusion that the reef ma- 

 terial may be 4000 feet thick on the Bahamas, and believes it may include 

 the entire Cenozoic section if not also the Upper Cretaceous. His conclu- 

 sion in theory if not in magnitude proved correct when the deep test 

 described above was drilled. It is concluded that most of the Bahama 

 platform area was a site of subsidence and deposition during the late 

 Jurassic, early Cretaceous, late Cretaceous, and parts of the Cenozoic. 

 The foundations of the Bahamas have been regarded as volcanic by 

 some; but this, in light of present stratigraphic and tectonic data, is onl) 

 possible below a depth of 15,000 feet. 



LESSER ANTILLES 



Divisions 



The Lesser Antilles, also known as the Caribbees, are an island festoon 

 that extends from the Anegada Passage on the north 430 miles to the 

 Island of Grenada on the south. See maps. Fig. 42.1 and 42. S. Several 



