270 bulletin: museum of comparative zoology. 



riddled with pot-holes, many of which have become connected to form 

 dumbbell-shaped cavities or other irregular forms (Plate XXIX.). They 

 are in every respect similar to the serpuline atoll pot-holes off the south 

 shore, but are much smaller, and become changed many of them into the 

 so called palmetto bases. 



An irregularly shaped pot-hole with a raised rim is one of the promi- 

 nent features of one of the ledges on the north side of the causeway 

 leading to St. George. In this case the greater hardness of the rim has 

 formed the protective coat for the low vertical wall of the pot-hole 

 (atoll). The transformation is readily followed in the pot-holes which 

 are a little removed from the immediate action of the diminutive, but 

 short and sharp, breakers of Harrington Sound. The inner cavity of 

 the pot-holes becomes lined with a harder coating, being acted upon 

 much as is the surface of the seolian rock. When the walls of adjacent 

 pot-holes are eaten away or worn away by the action of the rains and 

 of the sea, there may be formed an outer coating from the adjoining pot- 

 hole, and thus an irregular cylinder will be left standing above the sur- 

 rounding area. If the upper part of this is in turn disintegrated, we 

 may have left a deep cup, or merely a ring of the base, or a side of the 

 cylinder, or merely the harder inner coat of the bottom, — all of which 

 stages resemble more or less the base of a palmetto (Plate XXX.). 

 These pot-holes are often so close together (Plate XXIX.) that it is dif- 

 ficult to imagine a grove of palmettos the stems of which could be 

 packed in the area occupied by the pot-holes. Captain Carr, R. N., 

 called my attention to a locality on the east shore of Ireland Island 

 where these pot-holes are numerous, and where one can trace all the 

 transition stages just described from the pot-holes of the shore of Har- 

 rington Sound. 



NORTH ROCK. 



Plate VIII. 



The North Rock is undoubtedly the most interesting monument left 

 of the former extension of the Bermudian land. Owing to the difficulty 

 of landing, it has not been visited frequently, but we were twice success- 

 ful in landing at the North Rock Ledge. 



Excellent descriptions of the North Rock pinnacles and ledges have 

 been given by Rice, 1 and also by Heilprin in his volume on the Bermudas. 



1 Bulletin of the National Museum, No. 25, p. 14. 



