APPENDIX 



503 



precipitation in sea- water these materials have formed " nuclei " 

 for the development of oolitic grains. 



The foundations of the ceolian rock or wind-blown oolite of the 

 Bahamas (p. 262). — In reply to a question put by the writer, Dr. 

 Vaughan states that in the western islands the wind-blown oolite 

 rests on a foundation of marine oolite, and that in no instance did 

 he find " really coral reef rock interbedded with the oolitic rocks." 

 He adds that " after the (submarine) formation of the oolite, prob- 

 ably during a period of uplift, considerable quantities of material 

 were blown up by the wind and formed the dunes." These wind- 

 blown materials gave rise to the more or less compacted aeolian 

 rocks ; and it would seem to the present writer that a critical point 

 of first importance would lie in the determination by borings and 

 other methods of the relation of the level of the base of the wind- 

 blown rock with reference to that of the sea. According to his 

 view the junction of the wind-blown with the marine oolite would 

 be found at or about the present sea-level; but if, as held by A. 

 Agassiz, there has been a subsidence of 300 feet since the formation 

 of the islands, it would be found far below that level. 



The non-existence in South Florida of the calcareous ceolian oolite 

 of the Bahamas (p. 273). — It is a very significant fact that, as 

 Dr. Vaughan has informed the writer, this formation does not exist 

 in South Florida. Yet the islands of the neighbouring Bahamas 

 from end to end of the great archipelago are composed of this forma- 

 tion. There are extensive areas underlain by the marine oolite in 

 South Florida, but no wind-blown oolite is known. The sands 

 strewn over the interior of the peninsula, as well as those of the coast 

 dunes, are mainly siliceous. 



The ocean-holes of the Bahama Banks (p. 258). — Dr. Vaughan 

 tells me that A. Agassiz was undoubtedly correct in his inference 

 of a considerable subsidence, which was based on the occurrence 

 of these holes in the banks. With much diffidence I would suggest 

 that their preservation during the ages that have since elapsed 

 presents a difficulty, since it is not easy to perceive why they were 

 not obliterated during the great destruction of the land-surface 

 that, according to Agassiz, accompanied the submergence and by 

 the accumulation of debris and the growth of marine organisms in 

 later times. These ocean-holes are described as representing blow- 

 holes, sinks,, caverns, canons, etc., in the original land-surface. 

 Some of the smaller holes may have vertical sides with a sheer drop 

 of ten fathoms and more, and one might imagine that the same 

 submarine influences that produced them are still preserving their 

 patency. 



A suggestion of the present writer for the comparison of the behaviour 

 of sand-dunes of different mineral composition. — It may be that 

 we cannot strictly compare the movement of sand in dunes formed 

 of calcareous oolitic grains with that of sand in dunes derived from 

 the disintegration of volcanic rocks, such as has been described in 

 Note 34 of this Appendix on the moving sand-hills of the Ancon 

 plains of Peru. A comparison of the two kinds of moving sand- 

 hills on the lines adopted in that note may be suggested. In the 



