676 



STRUCTURAL GEOLOGY OF NORTH AMERICA 



spicuous in the western and central provinces. Overthrusting is described 

 in several places along the northern margin of the island (Fig. 42.4) and 

 presumably occurred at this time. All thrusting is now believed to be 

 toward the north. It is not known whether or not this mid-Eocene thrust- 

 ing of Butterlin is the same as the very Late Cretaceous thrusting of 

 Wassail. 



Orogenic movements then probably spread to the southern part of the 

 Province of Oriente. ... It should be added the upper Eocene begins with 

 conglomerates. Recurrence of volcanic activity is shown by the presence of 

 tuffs and of subsidence basalt dykes, thereupon marls and limestones (San Luis 

 formation) forming a deposit. In the Guantanamo Basin are found thick shales 

 of the same period (Guantanamo formation). At the end of the middle Eocene, 

 in the central and western areas, the sea appears again depositing at first 

 conglomerates and sandstones and, afterwards, limestones and marls (Loma 

 Candela formation). During the upper Eocene, the sea still progresses and if 

 littoral series (conglomerates and marls of Jabaco formation) are found, deep 

 deposits prevail (marls of the Jicotea group of the Jabaco formation and pelagic 

 marls of the Consuelo formation (Butterlin, 1956). 



Hispaniola 



Physiography. Haiti and the Dominican Republic make up the island 

 of Hispaniola, which is the second largest of the Antilles. It is about 400 

 miles long and in its widest part 160 miles. The greater part of the island 

 is ruggedly mountainous, with three or more of the clearly defined north- 

 ern ranges trending N 60° W. The axial or Sierra Central reaches an alti- 

 tude of 10,249 feet. This is the highest peak in the West Indies. 



North of Hispaniola is a narrow submarine trough with a general depth 

 of 12,000 feet, and beyond this is the shallow platform of the Bahama 

 Islands. See Fig. 42.1. Eastward the trough leads into still deeper water, 

 the Puerto Rico trench. South of Hispaniola the narrow shelf soon drops 

 off into the deep water of the Caribbean Sea. Cape Beata is a southward 

 projecting peninsula which continues as a submarine relief feature, the 

 Beata ridge, into the Caribbean basin, and divides it fairly well into 

 eastern and western parts. 



The intermontane valleys are thought by some to be of fault origin. 

 This is especially true of the Cul de Sac and the Basin of Enriquillo. 



Stratigraphy and Structure. The oldest rocks of Hispaniola are meta- 



morphic and igneous rocks which according to the present literature make 

 up the axis of the Cordillera Central and a large part of the northeastern 

 peninsula of Samana. See Fig. 42.5. Greenstones and amphibolites also 

 occur in the northern part of the island and may be a part of the ancient 

 complex. The quartz diorite is said to be of batholithic proportions. 



A new study of the complex has been made by Carl Bowin and he 

 reports on it in a letter to the writer as follows: 



Metamorphic rocks occur in central Dominican Republic at the eastern end 

 of the Cordillera Central and continue westward along the northern flank of 

 the Cordillera Central. These metamorphic rocks are probably of early Lower 

 Cretaceous or pre-Cretaceous age although direct evidence as yet only proves 

 a pre-Tertiary age. Thus in central Dominican Bepublic the oldest rocks do not 

 form the core of the Cordillera Central (as would be concluded from previous 

 reports), but flank the high mountains on the east and north. Towards Haiti, 

 however, the metamorphic rocks may make up the high mountains of the 

 Cordillera Central. 



Schistose limestone and quartz-calcite-chlorite-muscovite schists of unknown 

 age are found on Samana Peninsula. The foliation in these metamorphics is 

 reported to trend east-west. Metamorphic rocks are known in the basement 

 rocks that crop out near Puerto Plata on the north coast. However, the litholo- 

 gies present and their relations are but poorly known. Pre-Tertiary (?) argillites 

 are reported to occur on the south flank of the Cordillera Central and on the 

 south slope of the Cordillera Septentrional, but the grade of metamorphism 

 represented, if any, is unknown. 



A large serpentinized periodotite mass occurs in the metamorphic belt in the 

 central part of the country. The intrusive extends northwestward from north 

 of Ciudad Trujillo for a distance of 95 kilometers. A few small peridotite masses 

 are found in the metamorphics along the north flank of the Cordillera Central. 

 These appear to be the westward continuation of the large peridotite mass in 

 central Dominican Republic. Another serpentinized peridotite intrusive, trending 

 N 75° W, has been traced for 80 kilometers along the north coast. A few small 

 bodies of peridotite occur in the eastern portion of the island. 



The most detailed work on the pre-Tertiary rocks of the island of Hispaniola 

 has been carried out in central Dominican Bepublic. Here the metamorphic 

 belt trends NW-SE and consists of primarily epidote amphibolite and schistose 

 siricitic quartz keratophyre. The epidote ampribolites are intruded by sev- 

 eral plutons of leucocratic muscovite tonalite and two plutons of gabbro. 

 Both igneous types are probably of early Lower Cretaceous or pre-Cretaceous 

 age. 



The amphibolitic rocks are in fault contact with Upper Cretaceous (Ceno- 

 manian to Maestrichtian) unmetamorphosed volcanic rocks to the west. These 

 Upper Cretaceous volcanic rocks make up the high mountains of the eastern 



