160 FIELD COLUMBIAN MusEUM—GEOLOGY, VOL. I. 
utary to the cities of Mariquita and Ibague. The volcano of Tolima, 
according to Reclus, is an andesite cone upon a base of mica schist 
and slate. The mines are in part in andesites, other acid eruptives 
and their derivatives, which came from Yolima and various old vents 
of the vicinity, and in part in the underlying crystalline schists 
and slates. In the latter the ores tend to become poor for causes 
which will be explained later. The ores yield an auriferous silver 
and from them many secondary auriferous gravels have been derived. 
The minerals of these ores, like those of the Zancudo mines of 
Titiribi and Sabalétas, are mostly blende, which occurs with smaller, 
but yet considerable, quantities of galena and pyrite. Arsenical 
minerals are rare, but antimonial ones common. Pyrargyrite is a com- 
mon ore. These minerals occur principally in quartz veins, but 
much calcite occurs in the gangue in places and there are deposits in 
which brecciated country rock is the principal veinstuff. 
While some of the mines now in operation were reopened as early 
as 1785, many of them appear to be of very recent origin, as the 
towns in which they are located are not yet on the maps or mentioned 
in any works on the subject which are available. 
Mariquita, about ten miles west of the important city of Honda, 
is in the extreme northern part of Tolima. It hes on a plain in 
the valley of the Guari, which flows into the Magdalena from the 
west, and in the angle formed by the meeting of a ridge of the Central 
Cordillera, running east and west, with one running north and south. 
It was founded, according to Vicente Restrepo, in 1551, on account 
of the mines, and speedily became a very wealthy and important city 
of 20,000 inhabitants. With the decay of the mines its importance 
decreased, until it is now (as described by Reclus) an unimportant 
place of 5,000 inhabitants. The tributary mining districts stretched, 
in former times, for long distances to the south and east. Of these 
districts, only those of Santa Ana, Frias and Venadillo continued 
working mines in 1893, and consequently only these are represented 
in the collections, It is not unlikely, however, that some of the new 
districts may lie upon the site of the forgotten older districts. The 
chief product of the region is an auriferous silver. The placers are 
said to be rich in gold, probably from the decay of the auriferous 
silver deposits. 
