Most of the Island Realm and the mountainous backbone of the Mainland were formed during 2 mountain building periods. The first occurred around 70 million years ago froming the mountains of western Mexico and Central America and the low-lying outer islands of the Lesser Antilles.

DESCRIPTION OF LANDFORMS

The mountains of Middle America can be seen on the physical map of Middle America. There are also two "submerged" branches of these mountains running under the Caribbean Sea. One branch [see "trenches"] extends from the mountains of Guatemala, across the Caribbean (note the shallow water ) throught the Caymen Island, and can be seen as the Sierra Maestra Mountains of southeastern Cuba. This branch continues along northern Hispaniola, including the Cordillaera central, to the isalnd of Puerto Rico.

The Second branch begins with the mountains of Honduras, continues under the Caribbean to jamaica and on to the southern peninsula of Haiti, meeting the more thortherly branch at Puerto Rico. These mountains contiuea as a single branch through the low-lying OUTER ARC of the Lesser Antilles and connect with the Andes Mountains of south America in north eastern Venezuela

Between and along these mountain branches are deep ocean trenches. The Caymen trench can be clearly seen between the shallow water formed by the mountain branches. (See map "trenches" between the Caymen Islands and Jaimaica.) the Puerto Rican trench which is the deepest part of the Atlantic Ocean (deeper than the height of Mt Everest) lies along the north coast of Perto Rico and the Lesser Antilles.

WHY?

To understand the basic physical structure of Middle America one must have an understanding of plate tectonics. (For a longer discussion of plate tectonics see: http://pubs.usgs.gov/publications/text/dynamic.html

The earth's crust is made of of several pieces called "palates (world plates) that move very slowly. Originally this was called the Theory of Continental Drift (drift). Collisions of these plates can form trenches and mountains. These plate collisions also result in earthquakes and volcanoes. The world's location of earthquakes coresponds well with these plate boundaries (quakes).

Seven plates cam be found in Latin America (seven). Collisions of these plates result in subduction zones forming trenches and adjacent mountains. In Latin America the Peru-Chile trench along western South America is associated with the Andes Mountains. The Central American trench is associated with the mountainous backbone of that region. In the Caribbean, the Caymen trench and Puerto Rican Trench is found along the collision boundary of the Caribbean and North American Plates. Subjuction zones in these areas on plate i