MUSEUM OF COMPARATIVE ZOOLOGY. 279 



ample. It is an approximately circular, almost completely landlockerl basin, 

 communicating with the sea through a narrow but deep passage between broken 

 walls of the coral rock. The larger harbors departed from this plan chiefly in 

 their more irregular outlines, all agreeing in having deep, narrow mouths- 

 Every harbor is at the mouth of one or more rivers, and their inlets, as I con- 

 ceive, are the work, not of the sea, but of rivers at a time when tlie land was 

 higher than now. While the main body of the harbor, in each case, is simply 

 tlie broader and older portion of the river valley behind the barrier reef, which 

 has been invaded liy the rising sea, the circular form of many of the smaller 

 harbors is largely due to the fact that the sand brought down by the rivers is 

 thrown up by the sea into curved bars, cutting off the inequalities of the shore. 



" During the formation of the most recent of the elevated reefs, which, as 

 already stated, forms a level about thirty feet above the sea, the mouths of the 

 smaller streams were behind the reef, discharging into irregular channels or 

 basins between the reef and the shore. On account of the turbidity and fresh- 

 ness of the water, the reef, especially on its inner border, grew less rapidly at 

 these points than elsewhere, the basins behind the reef becoming filled with 

 debris from the land. "When the reef was finally raised to something above its 

 present level, each river scoured out a large part of the sand and gravel which 

 it had deposited, and cut a narrow channel through the reef itself. During 

 this period of elevation, Cuba, like most rising lands, had few harbors, but 

 when subsidence began the sea occupied the channels and basins which had 

 been excavated and cleared out by the rivers, and thus a large number of har- 

 bors came into existence. 



" Opposite the mouths of larger rivers, such as the Toar and the Molasses 

 in the vicinity of Baracoa, the reef in question w\as interrupted, and these 

 streams discharged into broad, open bays, while the lower portion of their 

 valleys show equally with the harbors that the land is sinking. They are half- 

 drowned valleys filled to a considerable depth with land detritus, conditions 

 ■which could not exist if the land was rising or had risen." ^ 



The interpretation of Ihe evidence of the harbors depends upon the 

 correctness or incorrectness of Mr. Crosby's hypothesis that the narrow 

 outlets through the reef rock represent a channel cut by the scouring of 

 the rivers themselves. It may be that they are channels representing 

 originally areas of non-coralline growth, such as ai'e now known to exist 

 in submerged reefs remote from areas with developed land streams and 

 in atolls, and such as biological laws tell us should exist opposite the 

 mouths of rivers, — such channels as now exist off shore around the coast 

 of Cuba, where reefs are growing. Mr. Crosby admits that the reefs 

 grew less rapidly at these points than elsewhere, on account of the 

 turbidity of the waters. 



The channel of the Havana harbor and the canon of the Yumuri 



1 Op. cit. 



