42 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



feet below low-water level. Ocean-holes were formed in a similar way at 

 a time when that part of the bank where they exist was above high-water 

 mark, and at a sufficient height above that point to include its deepest 

 part. Tlie subsidence of the bank has carried the level of the mouth 

 and of the bottom of the hole below high-water mark. 



From the description of the strata which crop out upon the banks in 

 the vicinity of some of the ocean-holes at Blue Hole Point, there seems 

 to be little doubt tliat the stratification characteristic of the aeolian rocks 

 has been observed. 



The principal ocean-holes, Blue Holes, are the following : one five to 

 six miles from Hawk's Bill Rock ; three, of eighteen, twenty-four, and 

 thirteen fathoms, a little east of north of Blue Hole Point, each about 

 five miles apart on a northerly line; and two, of seventeen and thirty- 

 eight fathoms, in the extension of the line of Blossom Channel leading 

 from the Tongue of the Ocean upon the bank. 



I am able, thanks to the kindness of Captain Wharton, the Hydrog- 

 rapher to the Admiralty, to give three sketches of these Blue Holes, 

 showing the character of the soundings around them (Plate III.). They 

 are such as we should expect to obtain from any part of the cays where 

 there are many light-holes, if sunken below the level of the sea. 



At other places on the banks ocean-holes are said to exist. Among 

 those not on the charts, I may mention a fifteen fathom hole at High 

 Point, Andros, and a twenty fathom hole in the Middle Bight, between 

 Gibson Cay and ]>ig Wood Cay. Dr. Northrop has examined some of 

 the ocean-holes of Andros, and has given a description of those he 

 visited.^ 



Except in the case of some wells at Nassau, there has been no obser- 

 vation of geolian rocks at any great depth below the surfoce. At the Ber- 

 mudas the a'olian rocks have been traced in situ during the building of 

 the dry dock to a depth of over fifty feet. The presence there of trunks 

 of trees would imlicate tlie invasion of sand dunes at so^ne time, much as 

 they invade the gardens of the Bermudas at the present day. 



From tlie desci'iption of the Bermudas given by Pein,. Thomson, 

 Fewkes. and lloil[irin, there appears to me little doubt that we have 

 there repeated on the bank of the Bermudas the identical processes 

 which have been described in this paper, and tliat the Bermudas and 

 the Bahamas owe their present configuration to the same process of 

 waste which lias l)ecn going on during their subsidence ; tliat the so 

 called diminutive lagoons we find there are not lagoons iu the ordinary 



1 Trans. N. Y. Acad, of Sci., Oct., 1890. 



