I 



NOTES ON THE GEOLOGY OF THE BAHAMAS 41 



shown on cross section shows very plainly that the solvent action of the 

 water, following the path of the root, had been from within outward. 

 As these masses are conspicuous and characteristic, I would suggest 

 that they be called rhizomorphs ; and this name would also cover the 

 tubular masses that have evidently been formed in the same manner, 

 and which I have found in the ferruginous clays of New Jersey and 

 elsewhere. The action of the water in the latter case has been on the 

 iron contained in the clay. 



Dr. Dolley is inclined to think that the rhizomorphs were formed 

 while the sand was in a loose state; and while I do not deny that this 

 might be possible, I believe that all that I saw had been formed by the 

 roots penetrating the already hardened rock; and I furthermore found 

 no rhizomorphs being formed by the plants growing in the loose sand. 



Dr. Dolley also states^ that the "small islands exhibiting these 

 peculiar formations [rhizomorphs] are indications, therefore, of 

 erosion and subsidence." I admit the erosion ; but as the rhizomorphs 

 are found twenty and thirty feet above the sea-level, I think that 

 subsidence has taken no part in their formation. 



These rhizomorphs are not to be confounded with the cylindrical 

 masses described on Goat Cay, for the latter were vertical and did not 

 exhibit the concentric arrangement of the particles so plainly shown 

 in the rhizomorphs, which are found at all possible angles. And if we 

 suppose the masses on Goat Cay to be due to the same process that 

 formed the rhizomorphs, we must suppose that the roots that produced 

 them grew vertically downward, which is extremely improbable. It 

 may be well to state that a few rhizomorphs were found on Goat Cay, 

 and the difference between them and the cylindrical masses was very 

 marked. 



It might be asked, if these rhizomorphs have been formed in the 

 manner described, why is it that we do not find them everywhere 

 on the islands ? And in answer to this objection it may be said that 

 roots of most of the trees spread out over the ground or slightly under 

 the crust, but do not penetrate the rock; and that the roots of the 

 smaller plants are those that have formed the rhizomorphs, and that 

 these latter show only where there is but little vegetation, and where 

 the erosion is active and not helped by the roots of trees breaking up 

 the surface into blocks as described above. 



^ Loc. cit., p. 132, 



