MUSEUM OF COMPARATIVE ZOOLOGY. 279 
ample. It is an approximately circular, almost completely landlocked 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 the land was 
higher than now. While the main body of the harbor, in each case, is simply 
the broader and older portion of the river valley behind the barrier reef, which 
has been invaded by 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 
débris 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 was 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.” 3 
The interpretation of the 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 are 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 caiion of the Yumuri 
1 Op. cit. 
