NOTES ON THE GEOLOGY OF THE BAHAMAS 31 



SxjRTACE Deposits 



There is practically no soil either on New Providence or Andros, 

 except the little that collects in the caves and holes in the rock. From 

 the caves a large quantity of cave earth, has been taken and sold as a 

 fertilizer, with what result I do not know. I was told that guano had 

 been found on Andros, but I saw none. The earths I collected I have 

 treated with hydrochloric acid, and the results indicate a great varia- 

 tion in composition. In some, most of the material is soluble with 

 strong effervescence, but in others the residual, I suspect, will prove 

 greater than the soluble portion. The residue seems to be composed of 

 organic material, with some mineral constituents that contain an appre- 

 ciable quantity of iron. Dr. Waller, of the School of Mines, Columbia 

 College, has kindly offered to analyze my material, and we hope from 

 the results to draw some conclusions as to its origin. At present it 

 seems as if the earthy deposits are composed of the insoluble portions 

 of the coral rock mixed with vegetable particles. 



The absence of any large quantity 9f fallen leaves is very noticeable. 

 In the "Pine-yard," as the pine woods are locally called, we did not 

 see a single fallen pine, but the depressions in the ground showed 

 where one had formerly stood, and a long shallow trough plainly indi- 

 cated where the fallen trunk had lain. Desiccation and decay take 

 place with astonishing rapidity, and I believe that the deposits found 

 in the caves are greatly added to by the comminuted particles of dried 

 vegetable matter, and the residue of the decomposed portions, both of 

 which would be washed in by rain-water. 



On the "swash" on the west coast of Andros a peculiar ash-like 

 deposit was noticed that covered small circular areas. This, on exam- 

 ination, proved to be composed of soft elastic lumps coated with cal- 

 careous material. These lumps under the microscope were seen to be 

 composed of one of the small, probably fresh-water, algae that had 

 grown in the pools of water, and which had been left when the pools 

 had dried. 



Erosion 



One of the most striking geological changes taking place in the 

 Bahamas is the erosion of both the surface and the shore line of the 

 islands. 



