160 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
It will be seen that the Caribbean Sea is almost entirely surrounded 
on all sides except the east by mountains trending east and west, and 
by submarine ridges of the ‘Antillean type. Тһе Windward Islands, 
marking the eastern inlet of the sea, are largely old volcanic heaps. 
A distinet class of mountains independent of great lines of folding of 
the earth crust are the volcanoes. These have grown by extrusion and 
accumulation. Sometimes they are parasitic upon the folded mother 
systems, somotimes independent of them. They belong to the great aren 
of igneous eruptivity which, since at least as early as the beginning of 
Tertiary time, has marked the whole western half of the North American 
continent, the Caribbean, and the north and west sides of the Andean 
region. Although blending into each other, the volcanic ejecta of this 
great belt тау be classified for convenience into two distinct age cate- 
gories, which we may call the quiescent and the active voleanie groups. 
The active voleanie groups occur in four widely separated regions: 
1. The Andean group of volcanoes of the Equatorial region of western 
South America, rising above the corrugated folds of the northern ter- 
mination of the predominant South American Cordilleras. 2. The chain 
of some twenty-five great cinder cones which stretch east and west across 
the south end of the Mexiean Plateau, protruding parasitic-like upon the 
terminus of the North American Cordilleras. 3. The Central American 
group, with its thirty-one active craters, and growing diagonally across 
the western ends of the east and west folds of the Caribbean corrugations 
fringing the Pacific side of Guatemala, San Salvador, and Costa Rica. 
This is separated from the Mexican group on the north by a large non- 
volcanic area, the Isthmus of Tehuantepec, and on the south from the 
Andean volcanoes by the Isthmus of Panama, where no active volcanoes 
are found. 4. The chain of volcanoes of the Windward Islands, marking 
the eastern gate of the Caribbean Sea, and standing in a line directly 
across the eastern termini of the Caribbean Mountains, trending east 
and west, and parallel to the Central Amorican group similarly situated 
at their western termini. 
The Isthmus of Panama, the Pacific coast of South America west of 
the Atrato, the north coast of South America, the old voleanic areas of 
Northern Mexieo and the United States, and the Great Antilles, are still 
other regions in which volcanic activity has long been quiescent. 
The North American Cordilleran region, lying north of the Isthmus 
of Tehuantepec, is one of north and south folded sedimentaries, plus 
accumulations of volcanic intrusions and ejecta, and dominates a con- 
tinental area. 
