
Mar. 1899. THE OreEs or CoLomMprAa—NICHOLS. 139 
in quartz. The only specimen from this town collected by Sejior 
Gamba (88, E 1062), is a specimen of firm, unweathered quartz, 
with a few small crystals of arsenopyrite. It comes from the Con- 
stancia, one of the two oldest and most productive veins there. 
Between Amalfi and Santa Rosa de Osos, Senor Gamba collected 
the following specimens: 
‘*89. Porphyry from dikes in the road between Amalfi and 
Santa Rosa.” 
‘“‘90. Porphyry from dikes in the road between Amalfi and 
Santa Rosa.” 
‘‘gt. Porphyry from dikes in the road between Amalfi and 
Santa Rosa.”’ 
‘92. Syenite from the Porce River on the road between 
Amalfi and Santa Rosa.”’ 
The remarks under specimen No. 1 will apply to this ‘‘ syenite”’ 
as well. It is here considered to be one of the acid lavas. 
/ 
GOLD MINING DISTRICT OF SANTA ROSA DE OSOS. 
Santa Rosa de Osos y Remedios lies in the Porce Valley, south- 
west of Amalfi. It is situated at an elevation exceeding 4,700 feet, 
and has a mean annual temperature of only 58°. In 1880 its popu- 
lation was 10,000. It probably ranks third in importance of the 
mining districts of Antioquia, coming after Remedios and Titiribf. 
Ores are found in the so-called syenite, mica schist, and gneiss, 
according to Gamba. As before, syenite is to be interpreted as 
trachyte and andesite. Phonolite is mentioned from one mine. The 
deposits consist of quartz vetas de cajon. All deposits along the 
Porce Valley are said by Whitney,* to be quartz veins of the ordi- 
nary type. From this district Sefior Gamba collected twenty speci- 
mens, representing four mines. The series is as follows: 
‘93. Mica schist from Santa Rosa de Osos.” 
‘94. Colorado ore from the Trinidad mine.” 
‘95. Colorado ore from the Trinidad mine.” 
“96. Colorado ore from the Trinidad mine.”’ 
‘97. Colorado ore from the Trinidad mine.” 
‘<98. Undecomposed quartz from the Trinidad mine.’ 
‘‘g9. Undecomposed quartz from the Trinidad mine.” 
‘‘t00. Syenite.” | 
) 

*** Metallic Wealth of the United States,’ p. 109. 
