AGASSIZ: BERMUDAS. 



265 



HW. 



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Figs. 2,3. 



aeolian stratification has been obliterated by the cementing and solvent 



action of the sea water. If the base, the mushroom-shaped ledge, is 



stratified horizontally (Fig. 2) 



the result of the wash of the 



breakers upon any part of tlie 



top left unprotected will he to 



dig out circular or elliptical 



atolls (Fig. 3) like A or B. In 



one case, A, the atoll will have 



a rim of nearly the same width, 



while in the other case, B, if 



tlie softer parts of the top are 



on the lee side, the atoll will 



have a wider rim on the 



weather side from B to A, or 



a pot-hole may also be formed 



between A and B. The pot-holes of these circular atolls are usually 



from three to four feet in depth. But in some cases I have measured 



them between five and 



si.\ feet, and eveil more. '^' '^' 



In others they are only 

 a few inches deep. I 

 have not observed any 

 growth of Serpulge of 

 greater thickness than 

 from twelve to eighteen 

 inches. 



Should the aeolian 

 strata dip towards the 

 lee side (Fig. 4) a horse- 

 shoe-shaped atoll is 

 formed, as indicated by 

 the dotted line AB. 

 The I'im is widest at A, 

 Fig. 5, graduall}^ becom- 

 ing narrower and lower 

 tow^ards the lee side as 

 it nears B, the whole or 

 the greater part of the 

 ledge having been carried away by the pounding of the surf, leaving 



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