250 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
geologic history of this region. By examining the results of these pro- 
cesses we may possibly obtain some light upon the architecture of the 
Isthmian country, while the paleontologic data will give us the histori- 
cal facts. 
Predominance of East and West Orogenic Trends. — In the introduc- 
tory chapter of this paper we have outlined the general arrangement of 
the mountain systems influencing the topography of Tropical America. 
From the publications of Felix and Lenk upon the southern termina- 
tion of the Mexican Cordilleras,’ those of Dr. Carl Sapper on the Gua- 
temala-Chiapas province," of Sievers's map and résumé of the Caribbean 
coastal region of South America, and of my own,* we find a description 
in widely separated localities of the prevalent east and west trend. of the 
orogenic systems of the Great Antilles and the peripheral Caribbean lands, 
and the demonstration further that in this region there has been an area 
of late Tertiary mountain making, whereby a new system of mountains 
has been made directly tangential to that of the prevalent trends of the 
main North and South American Cordilleras. 
Excepting the gigantic eminences piled up by volcanic extrusion, 
beside which all other surface features seem trivial, this late "Tertiary 
mountain folding is the most conspicuous and far reaching event of all 
geologic history in Tropical America. Before it, however, other orogenic 
periods and results are manifest, concerning which we shall endeavor 
to present what little is known. 
Evidence Indicating the Existence of a Pre- Tertiary Orogenic Complex. 
— The granitic mountains of Oaxaca, Chiapas, and Guatemala, with their 
laterals of Paleozoic and Mesozoic rocks, apparently belong to one or 
more orogenic complexes of great antiguity in origin. It is immaterial 
here whether they are Archean or not, but they may in part antedate 
the Tertiary period, and seem to be of Pre-Cretaceous age, and give us 
a faint insight into the existence of an ancient land in this region. 
According to Sapper ° the Archean foundation along which is arranged 
the Paleozoic and Pre-Carboniferous complex of strata plainly shows iu 
two chief chains, lying to the north and south of Rio Motagua, while in 
the southeastern portion of the country they show in the spurs of a 
third chain. From these foundations stretching through the north are 
Carboniferous, Cretaceous, and finally the Tertiary strata. Besides, one 
1 “Ueber die tektonischen Verhältnisse der Republik Mexico,” Berlin, 1892. 
2 Op. cit. 8 Op. cit. 
4 National Geographic Magazine, May, 1890. 
5 Op. cit. 
