

hill: geology of JAMAICA. 221 



It is apparent that the borders of the region were indicated after the 

 Appalachian revohition, at which time protean lands existed to the 

 north and south in the then separate Americas. It is even possible 

 that corrugations of Pre-Mesozoic rocks now concealed may have at that 

 time underlain the North American Coastal Plain, and established the 

 fundamental trends of the Floridian, Mexican, Central American, and 

 Windward ridges, especially the long east and west Segovian ridge or 

 ridges of Guatemala, and its possible extension into Cuba and Haiti, 

 which constitute the most northern of the Tropical ranges. 



The Sierra Nevadan revolution, at the close of the Jurassic time, 

 undoubtedly played an important part in establishing the northwestern 

 barrier of the Mediterranean region, and creating a permanent nucleus 

 for the accumulation of subsequent lands against it. The present 

 abrupt termination of the trend of the Sierra in southern California, 

 and the absence of trends directly continuous therewith in northern 

 Mexico, does not necessarily imply that related uplifts may not have 

 occurred in the western Sierra Madre region of that republic concern- 

 ing which we now know so little, except that its diminishing summits 

 towards the American border, formulated by the later movements, are 

 trending towards the Colorado Plateau. There may be nucleal lines of 

 the older Nevadan trend in the Mexican region parallel to and en 

 echelon with the Californian Sierra. No trace of this revolution can 

 even be hypothecated elsewhere to the southward in the Tropical 

 American region. 



The Andean and Laramide (or Pocky Mountain) revolutions of late 

 Cretaceous and Eocene time, although synchronous in age, have not 

 thus far revealed continuity across the Tropical zone. As has been 

 shown, no possible protraction of their trends can be connected across 

 it. Neither can their trends anywhere be identified in Central America 

 or the West Indies, where, on the other hand, the orogenic trends are 

 directly across their paths and at right angles to them. The only visible 

 effect of the Laramide movement upon Tropical America was to add 

 another belt of land, the Mexican Plateau, to the previously existing 

 continental mass northwest of the region. 



The Antillean uplifts which occur in the West Indian region (Great 

 Antilles and Virgin Islands), Central America, and the Isthmus of 

 Panama and the ranges of the Colombian- Venezuelan coasts and islands, 

 constitute the members of the latest and most important mountain 

 movement, and one which produced the present configuration of the 

 resrion mentioned. 



