6 PHYSIOGRAPHY AND GEOLOGY 



either of corals or of moUusks, the position of which could not be satisfactorily 

 accounted for as resulting from the action of winds and waves, or hurricanes." ' 

 One of the results of these various researches was to establish the fact that 

 the Bahama Islands stood on a shallow, irregular, platform which rose out of 

 great depths, not only from the Atlantic on the east, but also from the bottom 

 of the West Indian region on the west. In order to account for the irregulari- 

 ties in the margin of this platform. Dr. J. W. Spencer published two papers ' 

 in which he argued that the Bahama Islands, together with the rest of the 

 Caribbean-Gulf regions had been formerly much elevated and during this period 

 of elevation had undergone considerable erosion so that its surface became 

 deeply dissected with river-valleys and canyons. Later, when the region sank 

 to its present position, these valleys were submerged and gave rise to the various 

 passages between the Islands as well as to the embayments which make the 

 outline of the Bahama platform so irregular. 



During the month of April, 1903, the senior author of this chapter made a 

 geological reconnoissance of a portion of the Bahama Islands, and later, during 

 June and July of 1903, while a Director of the Bahama Expedition sent out 

 by the Geographical Society of Baltimore, he, in connection with Dr. Miller, 

 examined further into the structure of the Islands. The conclusions which 

 seemed to be Justified by these studies' were published just after the return of 

 the Expedition." They were as follows : 



" The present survey has been able to determine that the material com- 

 posing the Bahama Islands is not entirely made up of wind-blown coral and 

 lime sand, but the lower portions of many of the islands, extending np to ten or 

 fifteen or twenty-five feet above the present level of mean tide, has been de- 

 posited by the ocean and contains marine organisms in large numbers. Above 

 this lies the deposit of wind-blown material which has up to this time been 

 • regarded as the sole type of deposit visible throughout the archipelago. 



" In regard to the question of elevation or subsidence, the survey has deter- 

 mined that both processes have taken place. The Islands were doubtless much 

 higher at one time than to-day, and it is equally certain that they were formerly 

 more depressed beneath the Atlantic Ocean than they are now. It is impossible 

 to say whether they are being elevated or submerged at the present time, as the 



'Tjoc. cit. 



= Reconstruction of the Antillean Continent, Bull. Geol. See. Am., 1895, vol. 6, 

 pp. 103-140, and Resemblance between the Declivities of High Plateaus to Those of 

 Submarine Antillean Valleys, Trans. Can. Inst., 1898, vol. v, pp. 359-368. 



"Science, N. S., 1903, vol. xvlii, p. 428. 



