GEOGRAPHIC RELATION OF THE THREE AMERICAS 179 
lean corrugations, which fringes the Pacific side of Guatemala, 
San Salvador, and Costa Rica ; this is separated from the Mexi- 
can group on the north by a large non-volcanic area (the isthmus 
of Tehuantepec), and from the Andean volcanoes on the south 
by an area (the isthmus of Panama) in which no living 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 Antillean mountains 
of east-west trend, parallel to theCentral American group similarly 
situated at the western termini of these mountains. In recent 
times all these giants of fire have built up vast piles of lava 
and cinder into lofty summits, which overwhelm in topographic 
grandeur the lesser but more significant orographic features of 
the region. 
The quiescent volcanic regions, where activity was dominant 
chiefly in Tertiary time, but ceased long ago, are many. The 
isthmus of Panama, the Pacific coast of South America west of 
the Atrato, the northern coast of South America, and the old 
volcanic regions of northern Mexico and the United States are 
among these. There can be little doubt that the tremendous 
outbursts of igneous material in Tertiary time, which domi- 
nated western Xorth America, extended in a great belt around 
the southern end of the North American cordilleras, crossing 
the Caribbean area to the Atlantic between the two continents. 
The North American cordilleran region lying north of the 
isthmus of Tehuantepec is one of north-south folded sediment- 
aries, plus accumulations of volcanic intrusions and ejecta (chiefiy 
Tertiary), and dominates a continental area. 
The Andean region of the South American continent is one of 
north-south folded sedimentaries, plus accumulations of Tertiary 
volcanic intrusions and ejecta, and dominates a continental area. 
The Caril)l)ean region, including Central America, the Antilles 
and the Windward islands, and most of the Venezuelan and 
Colombian coast of South America, is one of east-west folded 
sedimentaries, plus accumulations of volcanic intrusions and 
ejecta, but, instead of dominating a continental region, pradicalhj 
constitutes a mouittniaous perimeter surroniulluff the depressed basin 
of the Oirlhhean. These mountains were mostly made about the 
close of Tertiary time, and hence are newer than the chief con- 
tinental systems. 
Upon this arrangement of the three systems of mountain folds 
are chiefly dei^endent the great physical ditlenaices l)ctween 
