126 FIELD CoLUMBIAN MusSEUM—GEOLOGY, VOL. I. 
As an example, it may be mentioned that the local names now applied 
to the rocks of the mining regions of Colombia follow the loose classi- 
fication of the time of Humboldt and Boussingault. The name gran- 
ite, for instance, is applied to a dacite, and rhyolites, andesites, 
trachytes and their tuffs are known as porphyries and syenites. 
The collection also merits attention in that it approaches much 
more nearly than is usual the ideal of what a collection in economic 
geology should be. Such collections are usually made by the selection 
of specimens of rich ore accompanied by any choice or rare minerals 
associated with them, and throw little or no light upon the nature or 
mode of occurrence of the deposits. This collection differs in import- 
antrespects fromsuch. There was little attempt to secure showy speci- 
mens, and Sefior Gamba took great care to secure average ores and 
to collect specimens of the gangue, associated minerals and country 
rock. To truly represent the resources of a region it is not enough to 
have such selected specimens of ores and choice or rare minerals. An 
ideal collection should have specimens of each kind and grade of ore 
produced—of the gangue, of all associated minerals, of the country 
rock, of intrusives, and, in short, of all rocks and minerals which may 
be associated with the ores. These specimens should be so labeled 
that their relation to each other may be readily understood. The 
relation of the value of an ore deposit to its surroundings should also 
be shown when possible. For example, when a vein which is rich in 
igneous rock becomes poor in clastic material, or when the deposit is 
rich only in the vicinity of some intrusive rock, this may often be 
shown in the collection. Again, an ore may always be accompanied 
by some peculiar mineral, or may have some other easily recognized 
feature which may and should be shown in the collection. The 
classic instance of Dr. Jackson’s discovery of the emery deposits 
of Chester from finding margarite, which he knew was accompanied 
by emeryin Asia Minor, bears witness to the importance of a knowledge 
which may be imparted by collections made on the right plan. 
Besides the specimens, much information of value. may be gathered 
during the collecting, and should be put into convenient form so that 
it may be readily consulted. The collection prepared by Sefior 
Gamba originally fulfilled to a high degree the conditions of an ideal 
collection. Unfortunately, the account of the mining and geology of 
Colombia, which was written to accompany it, was entrusted to care- 
less hands and lost, and only a portion of the collection itself reached 
the Museum. The collection now in the Museum consists of 116 
specimens from the original 425, and they are accompanied by a manu- 
script catalogue of the original collection. It has been the purpose 

