212 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



mountains from the Gulf of San Bias 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 Bias 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 homogeneoiA 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 x 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 quart zite. 



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, 2 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" rocks intruding the Tertiary 

 strata have been reported in Jamaica by the official surveyors, 3 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. 4 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 Ge'ologie de l'Ancienne Colombie Bolivarienne, Berlin, 1880, 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, describes it as "near the line between granite porphyry and quartz 

 diorite porphyry, ... of the structural type very common in the laccolithic masses 

 and intrusive sheets of early Tertiary age in Colorado." 



