A. Agassis — Notes from the Bermudas. 



415 



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. The pot holes 

 of these circular atolls are usually from three to four feet in 

 the depth. But in some cases I have measured them between 

 five and six feet and even more. In others they are only a few 

 inches deep. I have not observed any growth of Serpulse of 

 greater thickness than from 12 to 18 inches. 



Should the seolian strata dip towards the lee side (fig. 4) a 

 horseshoe-shaped atoll is Hw m 

 formed as indicated by the 

 dotted line AB. The rim is 

 widest at A, fig. 5, gradually 

 becoming narrower 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 a high narrow wall 

 with a deep opening at B be- 

 tween its extremities. Should 

 the surf break through the 

 sides at E or F or both, we 

 should have curved vertical 

 walls left, apparently built up 

 by Serpulse, in reality walls of seolian rocks which may be dug 

 out as I have suggested, either in the case of fig. 2 or of fig. 4. 



In the case of a long and wide ledge we have formed upon it 

 a number of secondary pits and atolls or pot holes as indicated 

 by the heavy lines of fig. 6. Let the walls of these break 



Figs. 4-5. 



Pig. 6. 



through and form connecting pot holes of irregular outlines and 

 we obtain a vertical wall such as is indicated by the dotted line 

 of fig. 6. Such a figure is a diagram of one of the ledges of the 

 outer reef off the south shore. 



A flat ledge projecting from the base of a shore cliff is eaten 

 into in the same way by the surf (fig. 7) and we have formed a 

 circular reef with vertical walls, of which the top is protected 

 by Algse and Corallines or Serpulse with a pot hole at its deep- 

 est part of 8 feet. We might call this a diminutive barrier 

 reef. 



