A, E. Verrill—The Bermuda Islands; Geology. 149 
The rough and corroded appearance, often noticed on the surface 
of broken shells, is due, without much doubt, in nearly all cases, to 
the action of the digestive fluids of fishes and other animals that 
swallow the mollusks. In some instances similar effects may be due 
to acids generated by decaying vegetable matters, with which they 
have been in contact at the bottom. 
That no appreciable loss of the coarser bottom materials occurs 
through solution is evident, for if the carbonated waters were not 
already saturated, they would surely first dissolve the impalpable 
calcareous mud, which is everywhere present in larger or smaller 
proportions, and thus speedily become saturated with lime. Nor is 
45 
Figure 43.—Borings of Lithophagus appendiculatus, in hard limestone, about 14 
natural size. 
Figure 48a.—The same; a, one of the shells removed. 
there evidence that solidification of these sediments is taking place 
anywhere beneath the sea, by the deposition of the calcium carbon- 
ate from solution. 
The breaking up of the massive corals and the larger shells is due 
largely to the action of various kinds of boring creatures, which 
penetrate the basal and older parts of the corals and the thicker 
parts of shells and gradually weaken them till the action of the 
waves can reduce them to fragments. Specimens of the common 
brain-coral are sometimes found five to six feet in diameter. These 
are probably more than 150 years old.* They would doubtless grow 
* So far as known there is no definite limit to the duration of the life of the 
large compound corals. Were it not for accidents and enemies, such as borers, 
they might live a thousand years or more, for aught that we know to the con- 
trary. As itis, some of the Pacific massive corals become 20 to 30 feet or more 
in diameter, indicating ages of 500 to 800 years. 
