232 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



ancient, massive, black igneous rock, showing fully 1,000 feet of verti- 

 cally jointed material. According to Professor Wolff's determination 

 this is olivine free basalt, or augite andesite, which everywhere seems 

 to be the chief species of the older igneous rocks. 



Beyond La Gloria the road seems to have passed the culmination of 

 the gorge topography of the Central Mountain masses, and the Atlantic 

 slopes of the mountains projecting from the summit of Turialba are 

 encountered. The summits or combs of these numerous salients are 

 deeply serrated by drainage. At this station more massive igneous 

 rocks are seen beneath the superimposed sheets of ash and lava. The 

 old red clays again set in in the cuts east of this station. At Tucurita 

 (altitude about 3,000 feet) the alpine scenery continues, and the road 

 clings to the cliffs far above the river level. 



Disturbed Tertiary Sedimentaries. — A greenish looking flaggy forma- 

 tion is encountered near La Gloria, which, from the train, is very sug- 

 gestive of disturbed sedimentary rocks. One mile east of the station 

 the massive igneous rocks are again encountered. From Las Animas 

 (altitude 1,830 feet) to Lajunta (altitude 250 feet), a distance of only 

 twenty miles, the road descends through distorted and upturned sedi- 

 mentary strata of Tertiary age, as shown in the profiles and sections. 

 (Plate VI. Fig. 2.) The igneous rocks protrude in every direction 

 through these sedimentaries, and their debris is scattered over the surface. 

 This portion of the section clearly demonstrates that the Tertiary rocks 

 have been folded and elevated to a height of at least 2,000 feet since 

 their original deposition, and that they have been pierced by numerous 

 igneous protrusions. These Post-Miocene intrusives are quite distinct in 

 specific characters from those of Tertiary age, as will be shown later. 

 This section Mr. Sjogren studied in detail. The details on Plate VII. 

 show how thoroughly he did this work. The paleontologic and petro- 

 graphic determinations of Drs. Dall and Wolff render this section the 

 most complete we have of any portion of the Tropical American region. 

 At Guallava, the next station east of Las Animas, the Tertiary rocks 

 are of Vicksburg age, — according to Dr. Dall, — and, so far as known, 

 the only rocks of this epoch west of the Mississippi. At Bonilla Cliff 

 they are Upper Oligocene, like the Monkey Hill beds. 



Throughout this portion of the journey tremendous formations of 

 rolled boulders also occur, apparently interbedded with the Tertiary 

 sediments, and the whole valley of the river is filled with them. The 

 Tertiary clays are well shown just east of Torito, one mile beyond which 

 point the road and river for the first time emerge out of the gigantic 



