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 tlius 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 

 months into a deeper area between tlie shore and an outlying barrier 

 reef, as now seen in the harbor of Jaragua, or into reefless submarine 

 areas ])roduced in the following manney. The entrance of the fresh 

 water iut > tlie sea prevented the growth of reefs immediately opposite 

 the mouth of the river as for out as the freshening influence of the 



1 Op. cit. 



