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STRUCTURAL GEOLOGY OF NORTH AMERICA 



apparently conformably by Paleocene, and Lower and Middle Eocene tuff with 

 lenses of algal limestone. 



The eastern part of the Dominican Republic is composed predominandy of 

 fine-grained tuff and interbedded dark gray limestone. These rocks are as yet 

 undated, but are probably of Upper Cretaceous age. Upper Cretaceous sedi- 

 ments are reported from a few localities on both the north and south flanks of 

 the Cordillera Central. 



North and south of the Cordillera Central Eocene sections are dominated by 

 limestone. However, in the Cordillera Central and east of it, clastic sediments 

 and tuffs were deposited in earliest Tertiary. Thus in the earliest Tertiary there 

 was a zone of volcanism and uplift in central Dominican Republic. This zone 

 may trend WNW into Haiti parallel to the trend of the Cordillera Central. 



The Oligocene and younger sections of the Dominican Republic are domi- 

 nated by clastic sediments and reflect a complex history of uplift and basin 

 development. 



According to Rutterlin (1956) the Lower Cretaceous Tuff series of 

 Cuba spreads eastward through Hispaniola, especially in the northern 

 and central regions where andesitic tuffs, basalts, and andesites accumu- 

 lated. 



In the peninsula of southern Haiti thick pelagic limestones accumulated 

 whose fauna bespeaks a Senonian age. This is the Macaya formation. Thick 

 and widespread underwater basalt flows occurred just before and after 

 the limestone depositing epoch, and probably extended westward to 

 Jamaica. 



According to Rutterlin again, sea flooding and deposition of sediments 

 were resumed in Paleocene time and then lasted until mid-Eocene. Con- 

 glomerates, sandy shales, calcareous sandstones, and clastic limestones, 

 the Marigot formation, started the sequence, but these give way in places 

 during early and mid-Eocene time to chalky limestones. In the north- 

 western peninsula a trough spread to Cuba, and in it thick basaltic and 

 andesitic tuffs accumulated which alternate with thin calcareous layers 

 (Perodin formation). In other areas crystalline or detrital limestones 

 resembling the yellow limestone of Jamaica were deposited and make up 

 the Plaisance and Hidalgo limestones. 



In the northern and north-central regions a new disturbance set in. 

 Folding was accompanied by dolerite and granodiorite intrusions. It is 

 impossible to distinguish the folds of this orogeny from the older ones 

 (Rutterlin, 1956). 



Limestone deposition continued until late Oligocene when renewed 

 orogenic movements set in to last until the Quaternary. From this time 

 on throughout the Tertiary flysch and molasse type sediments accumu- 

 lated. Tight folding seems the dominant structure with overturning both 

 north and south (Rutterlin, 1956). 



Considerable attention has been given the longitudinal valleys or 

 basins between the main Sierras. Some, like Rutterlin, favor the view that 

 the mountains continued to rise during the late Tertiary and that a gravity 

 flow type of structure developed toward the basins. Woodring et al. 

 (1924) describe the bounding faults as overthrusts. Rich (1956) treats 

 the Cul de Sac as produced by recent upfaulting and upbowing of the 

 bounding mountain block. Rucher (1950) postulates a good deal of 

 strike slip along bounding faults as sympathetic fractures to eastward 

 movement of the great Caribbean block. Hess and Maxwell ( 1953 ) show 

 the southern peninsula and the Sierra de Rahoruca to have moved many 

 miles from a west-lying position to its present position, and hence a 

 wrench fault of great magnitude to lie along the south side of the Cul de 

 Sac and the Rasin of Enriquillo. Several have related the graben-like 

 depressions to the Cayman trench which projects to the Cul de Sac. 



Puerto Rico 



Physiography. The island of Puerto Rico is roughly rectangular and is 

 about 35 miles wide and 105 miles long. See Fig. 42.6. Its highest peak is 

 3750 feet above sea level, whereas the Puerto Rico trench immediately 

 north of the island is 27,972 feet deep. The absolute relief between the 

 two is thus 31,700 feet. The plateau-like ridge upon which Puerto Rico 

 occurs also supports the Virgin Islands to the east. The slope into the 

 trough is in the proportion of one mile vertical to thirteen horizontal. See 

 Fig. 42.1. 



To the south of the Puerto Rico and Virgin Island platform the bottom 

 slopes steeply and, within 55 miles, is 17,000 feet deep. This is the site of 

 a submarine trench that leads northeastward to the Anegada Passage. The 

 bottom of the trench is generally 15,000 feet deep but rises to about 3850 

 feet below sea level at the summit or Passage. 



To the west, Puerto Rico is separated from Hispaniola by the Mona 



