Geographic Character: Southern Division. 119 
The Atlantic coast land of Costa Rica is generally low and is character- 
ized by lagoons which have been formed by the action of currents opposite 
the river mouths. The Pacific coast rises higher. The interior of the country 
is diversified by mountains, plateaus and valleys. A great volcanic range ext- 
ends from north-west to south-east from between Lake Nicaragua and the 
Pacific Ocean to the center of Costa Rica, separating a narrow Pacific slope 
from the broader descent to the Atlantic. The summits of this range are the 
peaks of Orosi, 5200 (6000, 5055) feet; Rincon de la Vieja, Miravalles, Poas, 
8845 (8895) feet; Barba, 9335 feet (2845 m); Irazu, 10,850 feet (11,000, 
11,200 feet) (3414 m); and Turrialba, 10,330 (10,900, 11,350) feet. — The form 
of the southern half of Costa Rica is determined by the great range called 
Montana Dota, 7000 to 9000 feet in elevation, which extends from west to east 
nearly across the country and from which two branches extend south-eastwards, 
the one close along the Pacific coast, the other through the center of the country 
' rising in the Cerro Chiriqui 11,850 (10,150, 11,970) feet and Pico Blanco, 
11,740 (9650) feet above the sea. — These mountains, as far, as they have been 
examined, are found to be of eruptive origin, basalts and trachytes predominate, 
but extensive sedimentary rock formations are also found upon their slopes, 
as well as vast deposits of boulders earth and volcanic material. — The broad 
tablelands of San Jose and Cartago, elevated 3c00 to 4000 feet, are between 
the northern and southern masses of these ranges and this central plateau is 
the most important and as yet the only cultivated region of Costa Rica. The 
Atlantic Slope is drained by the Rio Frio, San Carlos and Colorado tributar- 
ies of the Rio San Juan and in addition by the rivers Reventazon, Chirripo 
and Chiriqui. The chief streams on the Pacific side are the Kespiin: Rio 
Grande, Waranjo and Rio Grande de Terraba. 
It is clear that the Caribbean Sea once joined the Pacific Ocean through 
the Valley of the Reventazon River and that in Mesozoic times the high lands 
of Costa Rica once formed part of a vast archipelago extending from Panama 
to Tehuantepec, the islands of which possessed volcanic cones, which by their 
activity filled up and connected the islands to form a mainland. Prof. WILLIAM 
M. GABB in his geologic sketch of the Talamanca Mountains says that the 
nucleus of the great Cordillera of the interior is formed by the granites and: 
syenites, which, like the sediment that covers them, are broken through here 
and there by dikes of volcanic origin identical with the eruptive material found 
on a greater scale in the northern part of Costa Rica. Along the Talamanca 
coast, calcareous deposits are found in horizontal layers and are probably‘ 
elevated coralreefs, a rock wich Professor Gabb calls “antillite” and which is 
developed in the entire Caribbean region. It belongs to the post-Pliocene 
formation, the last of the Tertiary series. The Costa Rican orographic system 
passes into Panama through the Cordillera de Chiriqui which traverses the. 
entire isthmus. Low passes break this cordilleran system into a number of 
loosely connected spurs and ridges. It seems certain that here the two oceans 
were formerly connected through a number of channels and that Panama like 
