HILL: GEOLOGY OF THE ISTHMUS OF PANAMA. 279 



24. Homstone. 



25. A fine grained reddish rock, which is composed of a microlithic 



glass with altered bands of microfelsite, much opal and chal- 

 cedony. Probably a trachytic glass. 



26. Basalt. 



27. Dacite or quartz-porphyrite. 



28. Augite-andesite or basalt. 



29. Further study required. 



30. Decomposed dark gray augite-porphyrite. 



31. Altered tuff, containing silicified feldspar and bisilicate fraL' 



ments. 

 (51.2) and (51.3) Basalt. Paraiso. 



(59) Xear the Rio Grande River, Costa Rica. Hornblende andesite. 

 (59 bis) Melaphyre or Basalt. 



(60) From the drift, Limon, Costa Rica. A greenish banded flinty 

 looking rock ; in the slide this is, however, all carbonate of lime, granular 

 with large rounded areas which may be replaced shell fragments. 



(64) San Jose, Costa Rica, from one mile south of suburb called San 

 Miguel. Consolidated shell rock with clastic grains of feldspar. [Cre- 

 taceous limestone. — R. T. H.] 



(65) Granite. Station east of Cartago called Siquieres, Costa Rica. 



(66) Costa Rican railway between Limon and Cartago. (Label lost.) 

 Hornblende-porphyrite or andesite. (66 bis) Melaphyre or basalt. 



(68) Hypersthene-andesite, glassy. Between Cartago and Limon, 

 Costa Rica. 



(70) Various igneous rocks between Cartago and Limon, Costa Rica. 

 Chalcedony. 



(70) Altered tuff with fragments of basic eruptives, lavas. 

 3. Holocrystalline quartz-porphyry or granite-porphyry. 



(71) Old igneous rocks in valley of San Jose, Costa Rica : 



1. Melaphyre. 



2. Enstatite porphyrite. 



(72) Eruptives, valley of San Jose, Costa Rica. Decomposed mica- 

 diorite-porphyrite. 



(73) Lava in rim of crater Irazu volcano, Costa Rica. Basalt. 



(74) Outer rim of the oldest crater of Irazu, Costa Rica. Basalt. 



(76) Juanvinas, Costa Rica. Olivine free basalt, or augite-andesite. 



(77) Loretta, between Las Animas and Pasqua, Costa Rica. Graf 

 augite-porphyrite or holociystalline augite-andesite. 



(78) Irazu volcano, Costa Rica. Greenish gray augite-andesite. 



