INTRODUCTION. vil 
Atlantic and Pacific coasts there is a comparatively narrow belt of low-lying country 
clothed for the most part with forest; but this is interrupted in many places by 
savannas, especially on the Pacific slope, and “ rastrojo” or second-growth woods, 
which are due to the land having been cleared and cultivated in former times. In the 
central portions of the country, where there is much less rainfall, the vegetation is 
poor, scrubby oaks, pines (which do not reach south of Nicaragua), euphorbias, cacti, 
yuccas, agaves, &c, predominating. The greater amount of rain on the Atlantic 
slope, as compared with that on the Pacific, also accounts for the much more luxuriant 
forests on that side. From Southern N icaragua to the Isthmus of Darien the elevated 
land becomes less extended, till in Chiriqui there is only the central ridge. 
The physical conformation of each political district, as gathered from recent works 
on the subject, supplemented by my own or Salvin’s observations on parts of Mexico, 
British Honduras, and Guatemala, and those of some of our collectors in the more 
southern republics, may be described thus * :— 
MEXICO. 
Mexico stretches about 1950 miles from N.W. to S.E., with a mean breadth of 
400 miles. In lat. 26° N. it is 1000 miles wide, while at the Isthmus of Tehuantepec 
it is but 130. A continuous mountain-range does not exist anywhere here which can 
properly be called the Cordillera of the Andes, an expression only current south of the 
Isthmus of Tehuantepec. About three-fifths of the country is occupied by a vast 
tableland, in the shape of a cornucopia, tapering to the south-east in the neighbourhood 
of Oaxaca. Scarps rise in many places considerably above the plateau, broken into 
ridges usually running from N.N.W. to S.S.E. The most continuous range is the 
Sierra Madre of the Pacific slope, which may be traced from Oaxaca to Arizona, and 
corresponding with it on the Atlantic side are the Sierras Madres of Nuevo Leon and 
Tamaulipas, at an elevation of 6000 to 7000 feet. These ridges are in many places 
clothed with pine and oaks; but the general character of the tableland itself is barren 
and arid, being only sparsely covered with acacias, cacti, agaves, yuccas, &c., while in 
the depressions where there is water are patches of poplars and willows. It may be 
well here to give the altitudes of certain points in this plateau, in order that the reader 
may form an idea of its average elevation: Mexico city, 7600 feet; Zacatecas, 
8000 feet; the town of San Luis Potosi, 6170 feet ; Durango, 6630 feet; Chihuahua, 
* Further remarks on the physical features of the whole region will be found in the Appendix to the 
Botanical portion of this work, iv. pp. 117-315 (1887). 
