AGASSIZ : BERMUDAS. 227 



water upon the lower part of the eeohan strata, and from being friable 

 and crumbling, as they are above the reach of the sea, have been 

 changed into a solid compact limestone, which rings under the ham- 

 mer and can be chipped off in sharp-edged flakes. Tiiis is simdar to the 

 hard ringing beach rock now forming, and does not, it seems to me, 

 indicate the position of the former sea border. Almost anywhere on the 

 south shore one finds the base of aeolian cliffs consisting of strata dipping 

 inward, changed as high up as the sea can reach, into this hard com- 

 pact ringing limestone. A similar " base rock " fringes all the Bahama 

 Islands ; inland at Nassau, as at tlie Bermudas, a few steps from the 

 shore inside of the " base rock," the reolian structure is clearly defined 

 in quarries and wells extending below the water line, but the sea, acting 

 merely by percolation, has not changed their thin edges and cemented 

 them as it has on the sea face of the shores where the strata are fully 

 exposed to the action of the sea, and are in addition exposed for a 

 longer or shorter time to the atmospliere during low-water periods or 

 during the intervals between consecutive breakers. 



Rice says of the locally called base rock, " that it does not uni- 

 formly underlie the softer rocks, nor is tliere any evidence that it is 

 older than they." ^ A part of the confusion between base and beach 

 rock seems to me to have arisen from considering the ledges of seolian 

 rock as reef rock, and from the fact that there are a few localities on 

 the south shore where beach rock is actually forming from aeolian rock 

 sand, derived from ledges in deeper water, mixed with broken shells and 

 fragments of corals and Millepores, all of which particles are cemented 

 by the deposition of lime held in solution in the water percolating through 

 its masses. 



Rice further says, " That there can be no absolute distinction between 

 beach rock and drift rock will be manifest from the consideration that 

 the two formations are in their origin strictly continuous." Yes, but 

 their origin is not the same; the beach rock of to-day is formed in great 

 part of the aiolian rock of former days. I would go one step farther in 

 believing that the base rock is by no means usually beach rock, but that 

 beach rock is a very local phenomenon, and is younger than the feolian 

 rock, and belongs to the present epoch, and has been forming at different 

 levels, as it is forming to-day in favorable localities, from the time the 

 islands began to subside, as well as before that time. I am at a loss to 

 know what Rice and Nelson can mean by reef rock, unless it be the 

 thin crust of coral growth upon the ledges. I am inclined to adopt 



1 Bull. Nat. Mus., No. 25, p. 9. 



