A GEE AT LESSON. 251 



But when that energy became feeble, and when at last it ceased, 

 the once powerful structure descended again to that lower level of 

 the inorganic, and subject to all its laws. Then, what the ocean 

 could not do by the violence of its waves, it was all-potent to do by 

 the corroding and dissolving power of its calmer lagoons. Ever 

 eating, corroding, and dissolving, the back waters of the original 

 fringing reef — the mere pools and channels left by the outrageous 

 sea as it dashed upon the shore — were ceaselessly at work, aided 

 by the high temperature of exposure to blazing suns, and by the 

 gases evolved from decaying organisms. Thus the enlarging area 

 of these pools and channels spread out into wide lagoons, and into 

 still wider protected seas. They needed no theory of subsidence to 

 account for their origin or for their growth. They would present the 

 same appearance in a slowly -I'i sing, a stationary, or a slowly-sinking 

 area. Their outside boundary was ever marching farther outward on 

 submarine shoals and banks, and ever as it advanced in that direction 

 its rear ranks were melted and dissolved away. Their inner boundary 

 — the shores of some island or of some continent — might be steady 

 and unmoved, or it might be even rather rising instead of sinkinor. 

 Still, unless this rising were such as to overtake the advancing reef, 

 the lagoon would grow, and, if the shores were steady, it would widen 

 as fast as the face of the coral barrier could advance. Perhaps, even 

 if such a wonderful process had ever occurred to Darwin — even if he 

 had grasped this extraordinary example of the " give and take " of 

 Nature — of the balance of opposing forces and agencies which is of 

 the very essence of its system, he would have been startled by the 

 vast magnitude of the operations which such an explanation demanded. 

 In its incipient stages this process is not only easily conceivable, but 

 it may be seen in a thousand places and in a thousand stages of ad- 

 vancement. There are islands without number in which the fringing 

 reef is still attached to the shore, but in which it is being "pitted," 

 holed, and worn into numberless pools on the inner surfaces where 

 the coral is in large patches dead or dying, and where its less soluble 

 ingredients are being deposited in the form of coral sand. There are 

 thousands of other cases where the lagoon interval between the front 

 of the reef and the shores has been so far widened that it is taking 

 the form of a barrier, as distinguished from a fringing reef, and where 

 the lagoon can be navigated by small boats. But when we come to 

 the larger atolls, and the great seas included between a barrier-reef 

 and its related shores, the mind may well be staggered by the enor- 

 mous quantity of matter which it is suggested has been dissolved, 

 removed, and washed away. The breadth of the sheltered seas be- 

 tween barrier-reefs and the shore is measured in some cases not by 

 yards or hundreds of yards, not by miles, but by tens of miles, and 

 this breadth is carried on in linear directions, not for hundreds of 

 miles, but for thousands. And yet there is one familiar idea in geol- 



