252 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
of igneous rock in the basement beds of the Culebra clays, if the latter 
be of Eocene age, testifies to the presence of basic igneous eruption 
somewhere near the beginning of the Tertiary, if not prior thereto. 
The Tertiary strata of the Chiapas-Guatemala region, according to 
Sapper, are interbedded with conglomerates of andesite, which must have 
been extruded prior to the Tertiary period, while in other localities the 
horizontal Tertiary strata are deposited directly on the andesites. 
There is but little doubt, as we have shown in the previous pages of 
this paper, that during the early Tertiary period itself tremendous vul- 
canism, probably accompanied by orogenic changes, took place; in fact, 
no doubt this was the scene of the most cataclysmio revolution of all 
geologic time and place. We know that the older Tertiary strata else- 
where than along the Isthmian section have been thrust through by 
igneous intrusion. Theralites, trachytic, hornblendic, pyroxene ande- 
sites, augite andesites, porphyries, and basalts have been pushed through 
these sediments, shattering them by thousands of dikes, sills, and other 
forms of intrusion. 
Theoretically, there is no reason to believe that some of these classes 
of rocks did not exist before the Tertiary period. We know that at, or 
just after, the close of the Cretaceous, the igneous rocks which mark the 
whole American Pacific Cordilleran regions in later times were being 
protruded in both the Andean, Central American, Mexican, and Rocky 
Mountain regions, and the data submitted in this report show that this 
action was taking place in the Isthmian region in early Tertiary time. 
The older basic eruptives continue eastward from thé Isthmus, appear- 
ing in trend with the Isthmus on the peninsulas of Goagira and Para- 
guana, which guard the mouth of the Gulf of Maracaibo, and in the 
outlying hills of Aruba, Curagoa, and Bonaire. They also appear along 
the 10th parallel, between the 68th and the 66th degrees, in a narrow 
belt south of Caracas. 
The “syenitic” and other deep seated granitoid rocks which have 
been intruded into the Eocene Tertiary are certainly later in origin than 
tives of the Eocene epoch and older than the later basic 
rocks of the volcanic plateaux. Their exact status in the Isthmian his- 
tory is still somewhat involved, but they occupy no uncertain position 
ill be shown in our report on Jamaica, 
in the Antillean sequence, as WI 
where they are directly coincident in age with the great Mid-Tertiary 
epoch of Antillean mountain making. 
We also know that since the Pliocene epoch while the gigantic vol- 
y the surrounding structure with 
the basic erup 
canic cones have continued to bur 
