288 THE ATLANTIC. [cHapP. Iv. 
round opposing objects, using the vortices into which the sand 
itself is thrown by swirls of the wind as nuclei, if they en- 
counter nothing more prominent or resisting, sufficiently ac- 
counts for the prevalence of saddle-back sections. 
One phenomenon of these limestones especially gives a false 
Fig. 73.—Stratified Aolian Rocks, Bermudas. 
