SALT KEY BANK. 217 



holes themselves show nothing very peculiar ; there are many 

 such upon these Keys — some large ones many yards in diame- 

 ter, and others quite small — evidently formed by the wearing ac- 

 tion of loose pieces of harder coral rocks thrown upon the Key by 

 great waves, and only occasionally set in motion by the waters 

 dashing over the Keys during heavy storms. The pot-holes 

 nearest the water's edge are the most recent, and are mostly 

 clean excavations, either entirely empty or containing sand and 

 limestone pebbles lying loose at the bottom of the holes. Some 

 of these excavations are circular ; others oblong ; still others 

 have the form of winding caves opeuing toward the sea, or upon 

 the surface of the Key. Beyond the reach of ordinary tides, 

 and of the waves raised by moderate winds, the pot-holes are 

 generally lined with coatings of solid, compact, and hard lime- 

 stone, varying from a thin layer to a deposit of several inches 

 in thickness, and folio wins; all the sinuosities of the cavities in 

 which they are accumulating. It is plain from their structure- 

 that these coatings are a sub-aerial formation, increasing by 

 the successive accumulations of limestone particles left upon 

 the older rock by the evaporation of water thrown upon the 

 Key when the ocean is so violently agitated as to dash over 

 the whole Key. Frequently the hollow of these coated pot- 

 holes is further filled with consolidated oolite ; or thin layers 

 of fine-grained oolite alternate with a coat of compact lime- 

 stone, throughout the excavation, which often has been filled 

 in this way up to the general level of the surrounding surface. 

 Occasionally these regenerated surfaces are again hollowed 

 out by the action of storms, and the result is a dismantled 

 pot-hole, in which their structure and the mode of their filling 

 is distinctly exhibited. ' 



"The stratification of the main mass of these Keys is very 

 peculiar. Though evidently the result of an accumulation of 



