HILL: GEOLOGY OF THE ISTHMUS OF PANAMA. 28 
mountain gorges. Two miles beyond this station massive igneous 
rocks again appear in the cuts beneath the débris and the immense 
bluff of rounded boulders, like those at Mata Chin upon the Isthmus 
of Panama. Near Peralto there is a wide flat valley in the foot-hill 
scenery, which, from a cutting, is seen to be made up almost entirely of 
these boulders. Five miles east of Peralto there is a long tunnel 
through an immense hill of rounded boulder conglomerate. Seven and 
a half miles east of Peralto the railway reaches the river valley at an 
altitude of 1,500 feet. Тһе sedimentary Tertiary rocks are seen in the 
bluffs on the opposite side of the river. At Pascaua another intrusive 
neck of massive igneous material projects through these Tertiary sedi- 
mentaries, which Professor Wolff determined to be Theralite.? 
We now enter the lower hilly country which lies on the Caribbean 
slope of the volcanic highlands of Costa Rica. This country topographi- 
cally resembles the surface of the Isthmus ; it shows the same pointed 
character of the hills, the same deeply eroded valleys, and the same 
vegetation. One mile east of the station last mentioned, at an altitude of 
880 feet, 150 feet of greensand marls very much resembling the Mindi 
beds of the Isthmian section are exposed in a eut. Two miles to the 
east the river again cuts sedimentary beds dipping to the eastward. 
At Los Lomas, altitude 740 feet, there are great bluffs of Tertiary 
greensand, the strata of which have a very strong dip of nearly 45 
degrees. Massive rocks project through the sedimentaries. The river 
is still in a cafon 1,000 to 800 feet deep. Just before reaching Lajunta 
the river өшін through a tuff resembling that of Bujio on the Isthmus. 
At Lajunta we are apparently out of the mountain passes, but the great 
bluffs of rounded boulder débris whioh have rolled down the slopes of 
the volcanic plateaus for ages seem to cover this lower country. 
At Siquieres, altitude 390 feet, 57 miles from Limon, the hills are low, 
not averaging over 200 feet in height, but the boulder bluffs continue in 
great profusion, 
In Cartago, at the house of Mr, Jones, the station agent, we saw a 
small specimen of white granite, which he informed me he had found up 
the Rio Siquieres, and had broken off of an immense boulder which lay 
in the river at that place. This stream is a small river which drains the 
eastern foot of the Atlantic escarpment of the Turialba volcano, and 
there is no reason to doubt that granitic rocks oceur at the base of 
this great concealing mass of igneous material, That such granites have 
existed beneath the Costa Rican voleanie complex is still further attestod 
1 See American Journal of Science, Vol. I. p. 201. 1896. 
