242 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
to the vast aceumulations of more modern igneous and sedimentary 
rocks of Tertiary and Post-Tertiary age, a foundation of granitic rocks 
occurring in east and west arrangement existed in the South Isthmian 
aud Central American region, extending in echelon arrangement from 
the longitude of Trinidad through forty degrees to near that of Aca- 
pulco, Mexico, directly across the path of the main continental trends. 
The Paleozoic Sedimentaries. — Except a few outcrops in northern 
Sonora fossiliferous Paleozoic rocks are unknown in the Mexican Plateau 
region south of the Rio Grande of Texas. Тһе Paleozoic foundation of 
the Mexican Plateau was completely buried beneath Cretaceous lime- 
stone sediments, and since the elevation of the latter above the sea 
erosion has not yet been sufficient to re-expose them. In fact, between 
the southern boundary of the United States and the Empire of Brazil 
I know of but one well defined region of authenticated fossiliferous 
Paleozoic rocks, and this is in the Republic of Guatemala and the adja- 
cent Mexican border region of Chiapas, where Dr. Carl Sapper! has 
shown the undoubted occurrence of a large series lying above the so 
called Azui granites. Не describes the existence of an extensive system 
of Pre-Carboniferous rocks, probably Silurian, above which are Carbo- 
niferous limestones containing 36 enumerated species of characteristic 
fossils. Above this is a series of strata between the Carboniferous and 
the Cretaceous, then undoubted Cretaceous, and finally the Tertiary. 
This Guatemalan section, including its continuation into Chiapas, is the 
only one in the whole Central American region where undoubtedly 
fossiliferous Paleozoic rocks are exposed. АП positive evidence of the 
existence of the Paleozoic rocks elsewhere south of the United States is 
thoroughly concealed by overlap, — in Mexico by the overlying strata 
of Mesozoie, and in Central America by the later igneous and Creta- 
ceous and Tertiary rocks. 
The Older Mesozoic. — In 'Tropical America as in the United States, 
owing to the absence of fossil remains, the old Pre-Jurassic Mesozoic 
is a problematic formation, and is represented by three small outcrops 
only. Two of these occur in Mexico. One of them is at Miquchuana 
in the State of Tamaulipas, as discovered by the writer." Ти these 
two localities, not only by occurrence beneath the Jurassic, but by their 
characteristic composition and red colors, they are analogous to the Red 
Beds formation of the Western United States. "The third locality, or 
group of localities, is in the State of Guatemala and Chiapas, where Dr. 
1 Op. cit. (see footnote 1, p. 259). 
2 American Journal of Science, Vol. XLV. p. 911, 1808. 
