Gold Deposits on the Isthmus of Panama. — Hetshey. 73 
AGE AND ORIGIN OF CERTAIN GOLD DEPOSITS 
ON THE ISTHMUS OF PANAMA. 
By Oscar H. Hershey, Freeport, 1)1. 
Nearly all the workable gold-bearing quartz veins of the 
isthmus of Panama, west of the line of the Panama railway, are 
found in two main belts one on the northern flank of the Cor- 
dillera de Veraguas and the other in the foot-hills belt on the 
southern side of the great sierra. Both are long and compara- 
tively narrow, and trend in an east-west direction, parallel to 
the main mountain axis. There is nothing singular about the 
occurrence of the gold or its mode of derivation in these belts, 
but the veins are of such recent origin, as compared with 
gold-bearing ledges in most other districts of the earth, as to 
be of more than mere local interest. 
The Cordillera de Veraguas, on the line of the old Santa Fe 
and Cocuya trail, about 120 miles west of Panama, is an im- 
mense igneous mass, probably twenty-five miles in width. Once 
a high narrow plateau, stream dissection has converted it into 
an extremely rugged mountain system with a crest-line 5,000 
to 8,000 feet in altitude, and valleys 1,500 to 2,500 feet in depth 
Three rock types are chiefly represented. Specimens of them 
have been identified for me by Dr. U. S. Grant, as follows: In 
the valley of the Rio Santa Maria, on the southern slope of the 
range, the formation is mainly rhyolyte of light color. On the 
northern slope there is a great massif of rock "compxosed most- 
ly of flesh-colored feldspar, with some biotite and perhaps a 
little hornblende or augite," appearing like some of the nephe- 
line syenytes. On the continental divide, locally known as the 
Sierra Balcazar, and again about the headwaters of the Rio de 
los Saltos and the Rio Santiago, on the northern edge of the 
mountain complex, there is another great massif, whose rock 
has been doubtfully identified by Dr. Grant as andesyte, al- 
though, upon closer examination, he thinks it may prove a 
trachyte or even a diabase. Dr. C. P. Berkey says it very closely 
resembles one of the diabases found at Taylor's Falls, Minn. 
As for myself, from an examination of the formation in the 
field, I prefer to consider it a diabase. The relation between 
the three rock types is not well made out, but the fine-grained 
diabasic portion of the mountain formation appeared to bear a 
relation to the crystalline rhyolyte and syenyte somewhat as a 
