The writer has increased the pleasure which he derives from mineral collecting and his knowledge of geology by following this plan of card indexing his collection. It has been found very useful in comparing of specimens and determining the correct locality when in doubt. In addition to the name and locality the following facts are indexed:

1. The name of the rock which forms the matrix of the mineral. Endeavor to name the rock as scientifically as megascopic methods will permit. If the name applied is the correct scientific one, note the fact, with source of the information. In case of metamorphism include the name of the primary rock and in case of contact metamorphism, the name of the igngous rock.

2. Type of formation—Accessory in igneous rocks, in meta-morphic rocks; contact metamorphic; minerals of amygdaloidal cavities, of miarolitic cavities, of vugs or vein cavities; and so on.

3. Geological Age.

Give age of the formation and of secondary action if it has occurred. The authentic age may often be derived from publications of the U. S. Geological Survey, but if this data has not been collected in a certain region, attempt to determine the age from field work of your own or of others, quoting authority.

4. The chemical composition of mineralizers when their aid in the production of the minerals is evident.

5. Exceptionally fine specimens from the locality belonging to other collections; describe exceptional qualities.

6. Any additional features of the formation you may observe during examination.

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