GEOLOGY AND GEOLOGIC HISTORY. 81 



The events since Miocene time have included elevation and erosion, 

 which were accompanied by pronounced faulting and folding and which 

 lifted the Cordillera Central considerably higher than it stands now and 

 brought into existence the Cordillera Septentrional, an uplifted block of 

 Oligocene and older strata bounding the Miocene deposits of Cibao Valley 

 on the north. Structural deformation of the Miocene strata, although not 

 great in the Cibao Valley, proceeded apace in the southern region, where 

 the beds were folded, faulted, and overturned. The great structural 

 valleys, such as San Juan, Enriquillo, and Cibao, were probably produced 

 during Pliocene time, and into them were carried the products of erosion 

 of the central mountain chain, which were laid down at or near sea level. 

 The work of block faulting in shaping the topography of Haiti and other 

 islands of the West Indies group has been described by Vaughan. 1 



The events of late Pliocene time include mild folding and repeated eleva- 

 tion and depression, accompanied by more or less movement, which has 

 continued down to the present and which produce the destructive earth- 

 quakes that occur from time to time. There is evidence of late vulcanism 

 in the sheets of basaltic lava that cover the Las Matas formation along the 

 upper valley of Rio Yaque del Sur. 



During Pleistocene time there was a period of quiet, gradual submer- 

 gence, which favored deposition of the "coast limestone," a marly porous 

 rock of a type common throughout the West Indies, made up largely of 

 reef corals of species still living in the Antillean seas. The "coast lime- 

 stone" has been elevated so as to form an almost continuous line of cliffs 

 along much of the coast and has undergone slight deformation. The 

 paleontologic evidence indicates that its beds slope seaward, the youngest 

 beds being exposed nearest the coast. These beds locally rest uncon- 

 formably on Miocene strata, which appear a short distance inland in the 

 province of Santo Domingo and in other areas to the east. 



The extent to which the coast has undergone subsidence and emergence 

 is indicated by sea-cut cliffs and terraces at different altitudes and by the 

 presence of recent shell beds on these terraces. The amount of displace- 

 ment differs at different places. Meinzer 2 reports that beds in eastern 

 Cuba containing Pleistocene or younger fossils have been found up to an 

 altitude of 200 meters above sea level. Doctor Berkey 3 has likewise found 

 widespread evidence of depression and reelevation in Porto Rico. Similar 

 evidence was found by our party, the best being seen near San Pedro de 

 Macoris, where a shell bed some kilometers inland stands at an altitude of 



'Vaughan, T. W., Geologic history of Central America and the West Indies during Cenozoic time: 

 Geol. Soc. America Bull., vol. 29, 1918, p. 618. 



1 Meinzer, O. E., Geological reconnaissance of a region adjacent to Guantanamo, Cuba (unpublished 

 report), quoted by Vaughan in Contributions to the geology and paleontology of the Canal Zone, Panama, 

 and geologically related areas in Central America and the West Indies: U. S. Nat. Mus. Bull. 103, p. 265. 



8 Berkey, C. P., Geological reconnaissance of Porto Rico: New York Acad. Sci. Annals, vol. 26, p. 60, 

 1915. 



