122 Lieut. Nelson on the Geology of the Bermudas. 



portunity of depositing the sand; and this procedure must necessarily be of 

 universal occurrence under similar circumstances. 



Once thrown down, unless carried off by a more powerful action than the 

 original one, every fresh layer of sand not only increases the obstacle, but 

 likewise the tendency to arrest the passing materials, until such time as a 

 limit is attained by the increased, and consequently destructive velocity of the 

 current in the thus narrowed channel. 



Assuming then any such initiative, as the head of a rock at the bottom of a 

 sea in which enormous districts of zoophytes, &c., abound, as between 32° or 

 34° on each side of the equator, and from which dead portions to a con- 

 siderable amount are incessantly torn off, and moved on with the waters until 

 stopped by the rock, there will then follow the continued operation of the 

 preceding law, of which this is the commencement. 



Zoophytes and other marine animals, of which the germs are passing on 

 with other matters, attach themselves, as my own observations enable me to 

 assert, indifferently to the first base they can find; and by their growth, re- 

 production, and death, add to the stability and bulk of the colony. In this 

 manner, I conceive* submarine mountains are constructed, and around their 

 summits, the coral reefs. 



If the tides have their usual action and alternate direction, then the 

 necessary form assumed by such a bank, will be like that of the average of 

 sand banks and coral groups, elongate, and more or less ovate. 



Such germs as are dispersed in the water, on touching the bank, will on 

 the whole collect in greater quantities on the declivities of the edges than 

 on the plateau of the upper surface, over which they are far more likely to 

 float away. Most zoophytes affect a vertical growth, and in this attitude have 

 a tendency to add to the accumulations of the exterior fence, to the prejudice 

 of the space circumscribed. 



Hence, I would surmise, is their generally annular form ; and as to their 

 somewhat uniformly level upper edges, that is of course regulated by the sur- 

 face of the tides, above which the animals cannot for any length of time exist. 



The Bahamas lie in the bight of the gulf-stream, and the Bermudas on its 

 outskirts; whether this is, or is not, the immediate parent of these groups, 

 if we admit the above premises, then once above water, the wind is sufficient 

 to complete districts of indefinite extent; and far larger than those which 

 have formed the subject of this Memoir. 



Although the stone has been described as forming rapidly at Elbow Bay, I 



* In some places the reefs interfered with the works ; and when destroyed in consequence, I 

 never saw sufficient reason to induce me to alter my views as above stated. 



