MUSEUM OF COMPARATIVE ZOOLOGY. 265 
northern coast, examples of which are common on all the pilot charts. 
Most of these are constructed upon the same fundamental type, consist- 
ing of a subcircular or reniform bay outletting through a narrow neck 
or strait into the sea. Into the back of the bay usually flow one or 
more of the small rivers of the country. Generally the landward side 
of these harbors is or has been the elevated, broken Cuchilla highland, 
while the points of the narrow necks enclosing the outlets to the sea 
are sub-level plains composed at the sea margin of soboruco or recent 
elevated reef rock. 
On the landward side of some harbors at the foot of the cuchillas, 
those of Havana and Baracoa, for instance, there is sometimes a playa, 
or alluvial plain of small area, composed of ancient sediments of the 
river, which has participated in the general elevation of the coast. 
The accompanying plate (Plate II.) enables us to discuss more intelli- 
gently these phenomena, and their bearing upon the elevation of the 
island. 
There are two possible hypotheses concerning the origin of these 
harbors. The first is that of subsidence and superimposition, as set 
forth by Crosby, given more fully in the portion of this paper treating 
of evidences of subsidence. This implies that the elevated reef rock 
once extended across the area now occupied by the neck or outlets, and 
at a former epoch of elevation was eroded through by the rivers, and 
that by subsequent subsidence the waters of the sea encroached upon 
the land through the channel thus worn, producing an estuary. A 
second hypothesis is that they are the result of the growth of fringe and 
barrier coral reefs adjacent to or opposite the mouths of rivers, which 
were subsequently elevated and unequally eroded. In my opinion, the 
harbors were evolved from the simple type of rivers now emptying 
directly into a fringed reefed sea, like that of the Rio Yumuri of Baracoa 
and the Limones. (Plate II. Figs. 1 and 2.) The rivers all originally 
emptied directly into the sea, as do the Yumuri and the Limones of 
to-day, and the coast line was the precipitous bluff of the Cuchilla high- 
land, now forming the background of these harbors, in front of which 
was a basal shelving beach. Delta material was discharged off their 
mouths into a deeper area between the shore and an outlying barrier 
reef, as now seen in the harbor of Jaragua, or into reefless submarine 
‘areas produced in the following manner. The entrance of the fresh 
water into the sea prevented the growth of reefs immediately opposite 
the mouth of the river as far out as the freshening influence of the 
1 Op. cit. 
