40 NOTES ON THE GEOLOGY OF THE BAHAMAS 



where in contact with the shoots, it had hardened into rock. This, 

 I believe, explains the ridges described above, for the roots are fre- 

 quently a foot below the surface, and the action of fresh water follow- 

 ing down the shoots, and probably, also, the action of the juices of 

 the plant, have slightly dissolved the calcareous material and then 

 cemented it into a rock harder than the surrounding deposit. The 

 latter, when erosion commences, wears away and leaves the harder 

 ridge standing. The manner in which the ridges are formed, and the 

 holes in the tops of them, all strengthen this conclusion. The trian- 

 gular spaces enclosed by the ridges are almost identical in appearance 

 with the triangular spaces marked off by the sucker-like roots that 

 cross each other in all directions. 



Rhizomorphs 



While visiting the quarry at Nassau my attention was drawn to 

 some cylindrical masses of coral rock that apparently hung root-like 

 over the edges of the quarry and were about four feet in length. They 

 were, however, cemented to the wall. I broke one off, and on examin- 

 ing it, found that the particles of which it was composed were arranged 

 in a concentric manner about a central axis. On the way back from 

 the quarry I pulled up a small shrub, and found its roots penetrating 

 the rock, which had been eroded so as to leave cylinders surrounding 

 them. Dr. Dolley 1 has called attention to these cylindrical and tubu- 

 lar forms, and has explained their formation by supposing that they 

 represent the "ramifications of a now exterminated flora," and also 

 that " the juices of the roots, acting on the sand immediately surround- 

 ing them, formed a compact layer. Through erosion and subsidence 

 the vegetation was afterward exterminated, the looser particles of drift 

 rock worn away, and the surface left covered by myriads of tubes of 

 all sizes, formerly occupied by plant roots and rootlets." Later, on 

 Spruce Cay, near Nassau, and at many other places, I found a number 

 of these cylindrical projections, some of which contained a small hole 

 in the center, which in others was filled with calcareous material. I 

 believe Dr. Dolley's theory of the formation of these cylindrical and 

 tubular projections is, in the main, the correct one; for I collected 

 specimens with the roots still in them, and the concentric arrangement 



1 Loc. cit., p. 131. 



