AGASSIZ: BAHAMAS. 7 



islands of the group. After the formation of the islands came an exten- 

 sive gradual subsidence, which can be estimated at about three hundred 

 feet, and during this subsidence the sea has little by little worn away 

 the seolian hills, leaving only here and there narrow strips of land in the 

 shape of the present islands. Inagua and Little Inagua are still in the 

 original condition in which I imagine such banks as the Crooked Island, 

 Caicos, and the Turk's Islands Banks, and other parts of the Bahamas, 

 to have been ; while the process of disintegration going on at the western 

 side of Andros still shows a broad island, which will in time leave only 

 the narrow eastern strip of higher aeolian hills on the western edge of 

 the Tongue of the Ocean. Such is also the structure of Salt Cay Bank; 

 it owes its shape to the same conditions as those which have given the 

 Bahamas their present configui'ation. My reason for assigning a subsi- 

 dence of three hundred feet is that some of the deep ocean-holes on the 

 bank have been sounded to a depth of thirty-four fathoms, and I take 

 them to be submarine blow-holes or canons in the geolian limestone of the 

 Bahama hills when they were at a greater elevation than now. 1 Subsi- 

 sidence explains satisfactorily the present configuration of the Bahamas, 

 but teaches us nothing in regard to the substratum upon which the Ba- 

 hamas were built. Indeed, the present reefs form but an insignificant 

 part of the topography of the islands, and they have taken only a 

 secondary part in filling here and there a bight or a cove with more 

 modern reef rock, thrown up against the shores so as to form coral 

 reef beaches such as we find in the Florida Reef. 



We steamed in the " Wild Duck " nearly forty-five hundred miles 

 among the Bahamas, visiting all the more important points, and made 

 an extensive collection of the rocks of the group. 



I had on board a Tanner sounding machine, kindly lent me for this 

 trip by Colonel McDonald of the Fish Commission, and some deep-sea 



1 Dr. John L. Northrop. ("Notes on the Geology of the Bahamas," Trans. N. Y. 

 Acad, of Sci., Oct. 13, 1890,) who passed considerable time in New Providence and 

 in Andros, has given an excellent account of the characteristic features of Andros 

 He considers the evidence he has collected as conclusive of the recent elevation of 

 Andros and of New Providence. During my extended examination of the Bahamas 

 I did not meet anywhere with deposits either of corals or of mollusks, the position of 

 which could not be satisfactorily accounted for as resulting from the action of winds 

 and waves, or hurricanes. On the contrary, the very facts Dr. Northrop brings forth 

 regarding the configuration of the western coast of Andros seem to me to lead to 

 the opposite conclusions from those arrived at by him. All the evidence I have 

 shows that the Bahamas owe their present configuration to subsidence and erosion, 

 and that they are not rising. 



