A.GASSIZ: BERMUDAS. 



265 



HW. 



L W tti 



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 the 



top left unprotected will be 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 



the 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 



six feet, and even more. Hw " m * 



In others they are only 



a few inches deep. I 



have not observed any 

 growth of Serpulce of 

 greater thickness than 

 from twelve to eighteen 

 inches. 



Should the seolian 

 strata dip towards the 

 lee side (Fig. 4) a horse- 

 shoe-shaped atoll is 

 formed, as indicated by 

 the dotted line AB. 

 The rim is widest at A, 

 Fig. 5, gradually becom- 

 ing narrower and lower 

 towards 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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