36 NEW YORK STATE MUSEUM 
System of lettering forms. Although the system of symbols hitherto 
described are essential to the expression of the relations between crystal 
forms of calcite, they are, particularly in the case of the Bravais indexes, 
cumbersome when applied to the designation of faces in crystal drawings. 
Extending back to the early literature of calcite the universal custom among 
crystallographers has been to assign a letter to each crystal form. As new 
forms were recorded and corresponding letters assigned to them this letter 
system soon outgrew the limits of the Roman letters, and Greek and Ger- 
man letters were resorted to. Some of the early writers introduced astro- 
nomic and alchemistic characters, and the French crystallographers for the 
most part lettered their figures with the Lévy symbols. These letters were 
assigned with no regard to the crystallographic relation of the forms and 
Were in many instances duplicated or, as in the case of the unit rhombohedron, 
the form was indicated by several different letters. Dr V. Goldschmidt* 
to obviate this confusion and to provide a rational and universal method 
has devised a system at once simple and comprehensive for lettering the 
forms of calcite. His scheme of lettering, which admits of considerable 
expansion to provide for the recording of new forms, employs the large and 
small letters of the Roman, Greek and German type, omitting certain 
letters which, from their similarity to others employed, would lead to con- 
fusion. In this way 133 characters are available. This number is, however, 
insufficient for the lettering of the upward of 300 recognized forms of calcite. 
Goldschmidt meets this difficulty by introducing a period, colon and a 
diacritical mark consisting of three vertical dots after the letters, thus 
increasing the number of available characters fourfold. These are assigned 
to the types of forms as follows: 
1 Prisms, pinacoids and pyramids of the second order are lettered 
with plain small Roman and Greek letters, thus a, «. 
2 Rhombohedrons are lettered with he and small Roman and Greek 
letters followed by a period, thus; A., a., Ay 
1 Goldschmidt, V. Index der Krystallformen der Mineralien. Berlin 1886. 
1:134, 141. 
