A Monograph oj Marcus. Island. 



85 



the sea the sides have become concave, while the angles have been 

 rounded down to form obtuse points. Beginning with the south 

 side we find the beach composed, for almost its entire length, of 

 coarse coral shingle, from which the finer coral sand or detritus 

 has been thoroughly sifted. The average size of the pebbles along 



Fht. 3. The northwest side, looking toward the north point. The birds are 

 the female and the downy young of the Booby, Sula sula (Linn.). 



the water line was probably half an inch in diameter. Back some 

 distance these bits of coral were considerably larger in size and 

 were not so worn and rounded. Immediately in front of the settle- 

 ment, between a salt water well and the sea, was exposed a table 

 of shingle conglomerate, the surface of which was some fifteen feet 

 or more above the sea. 



