276 BULLETIN: MUSEUM OF COMPAEATIYE ZOOLOGY. 



Preliminary Description op the Specimens of Igneous Rocks in 

 the Collections from the Isthmus of Panama and Costa Rica, 

 made by Robert T. Hill, January, February, and March, 1895. 



By J. E. Wolff. 



(2) Quarry* at Bujio. In the slide a much decomposed augite por- 

 phyrite. The slide must be from a pebble, for the hand specimen is a 

 conglomerate. 



(3) Boulders of hill back of Peha Negra, about one mile below Bujio 

 on Chagres River. Both slides are of hornblende andesite. 



(5) Cut north of end of Las Cascadas siding, Panama Railroad. A 

 reddish green granular rock, with green spots and chalcedone lining 

 cavities. Contaius fragments of feldspar and of eruptive rock. Silicified 

 tuff. 



(6) Panama Railroad, neck below " Nigger Head " Bluff, Mata Chin. 

 Basalt. 



(7) First cascade, Las Cascadas. A banded gray flinty rock. In 

 the slide long laths of plagioclase feldspar crystals of magnetite, and 

 abundant black irregular grains, probably the decomposed bisilicate. An 

 eruptive (augite -porphyrite 1). 



(8) Panama Railroad from Nigger Head Bluff, Bas Obispo. A decom- 

 posed basic eruptive hornblende-augite-andesite, or porphyrite. 



(9) 31st mile Panama Railroad. Augite-andesite. 



(10) 31 h miles Panama Railroad, Bluff near Haut Obispo. (?) Badly 

 decomposed olivine basalt, or melaphyre. 



(11) 33 miles Panama Railroad. First fall of the Obispo River. A 

 reddish gray trachyte with feldspar phenocrysts and green patches. 



(12) 32 miles Panama Railroad. Coarse decomposed tuff; augite 

 porphyrite fragments ; calcite cement. 



(13) 31 1 miles, Panama Railroad cut near Bas Obispo. Tuff with 

 siliceous cement and fragments of decomposed basic eruptives. 



(14) 344 miles, Panama Railroad. Empire cut. Limestone contain- 

 ing shell fragments. 



(15) Panama Railroad, miles 32, cut in east and west hill. Dirty 

 green decomposed augite andesite. 



(16) Panama Railroad. Drift from high mountain back of Empire 

 limestone, £ mile north. Dolerite (Basalt). 



(19) Panama Canal between Vamos a Yamos and 10£ kilometers. 

 A dark gray limestone containing shells. In a calcareous cement 



