212 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
mountains from the Gulf of San Blas and Caledonia Bay give the im- 
pression that the country is composed of the older Tertiary sandstone 
and clays which have been vertically folded and through which has 
been pushed a mass of *syenite." Furthermore the so called  syenite " 
is cut by dykes of basic igneous rocks. "This “syenitic” axis of the 
Cordillera San Blas is some fourteen miles in width, extends in an east 
and west direction, and is bordered on both sides by the sandstones and 
clays through which it has been intruded. 
The “syenite ” is described as a “hard gray dense syenite, portions 
of which have a very fine grained and beautiful texture." In places 
the rock is homogeneous in character ; at others it shows veins of quartz 
and large crystals of feldspar, and at one end is made up entirely of 
greenstone.” These geologists concluded that the “entire nucleus of 
all the mountains was syenitic, a fact fully verified at many points.” 
The Tertiary sandstones in places are highly metamorphosed, forming 
a quartzite. 
Around Santa Marta, longitude 74°, just east of the mouth of the 
Magdalena, the Sierra Nevada is largely composed of eruptive granite, 
described by both Sievers and Karsten. According to the latter," it 
appears that this granite has been erupted, has come from the depths 
in an incandescent state, and has elevated, folded, and dismembered 
the adjacent beds." 
Similar “granitic” and “syenitic” rock# intruding the Tertiary 
strata have been reported in Jamaica by the official surveyors,® which 
occurrence the writer has had opportunity to study. 
These many independent observations indicate a wide occurrence 
throughout the Tropical American mainland and the great Antilles of 
a Mid-Tertiary intrusive rock which has been considered granite or 
syenite.^ In the forthcoming report upon Jamaica the influence of this 
event in Tropical American geologic history, having great bearing upon 
the origin of the Antillean mountain system, will be described more 
completely. In Cuba and Hayti there are probably older granites. 
1 Carson and Bowditch, p. 137. 
2 Géologie de l'Ancienne Colombie Bolivarienne, Berlin, 1886, p. 23. 
8 Memoir Geological Survey of Great Britain. Reports on the Geology of 
Jamaica. London, 1869, 
4 Mr. Whitman Cross, of the United States Geological Survey, who has studied 
specimens of this material collected by the writer from the Blue Mountains of 
Jamaica, deseribes it as "near the line between granite porphyry and guartz 
diorite porphyry, >. . of the structural type very common in the laccolithic masses 
and intrusive sheets of early Tertiary age in Colorado." 
