LHE NAMING OFF ROCKS 697 
advancement of science, it will be sure to be retained. If it 
drops out of use, its proposal was premature. 
Summary of advantages of proposal—In conclusion, some of 
the advantages of the foregoing plan may be summarized: 
1. The plan proposed serves all the purposes of nomencla- 
ture, from names of a general character to those giving the 
most minute discriminations. It has the advantage of grouping 
different varieties of rocks under terms, the general meaning of 
which is known to all. In the matter of nice discrimination it 
far surpasses the plan of independent new names for new vari- 
eties of rocks. It permits at once any difference in the charac- 
ter of a rock, however slight, to be discriminated, and it permits 
the growth of petrography by the grouping of the allied varieties 
together under a new specific name so soon as they shall have 
been found so abundant, so peculiar, or so important as to 
demand such a name. The professional petrographer will thus 
have a much more convenient and elastic nomenclature for 
describing rocks than he has at present. He may ignore minor 
differences between rocks in one sentence, and in the next sen- 
tence deal with the most refined differences between them. Thus 
the plan advocated meets both the demands of the geologist and 
of the specialist in petrography. 
2. The plan proposed puts the available information of 
petrography in such shape that some master mind in the future 
may reduce the subject to a science. The present scheme of 
rock nomenclature makes it impossible for any person to get the 
facts clearly before his mind in such a way that they can be 
handled. The provisional scheme proposed accomplishes this 
end. If it be generally followed by petrographers, it is probable 
that within a few years it will be possible to propose a definite 
scheme of rock nomenclature, the terms of which correspond 
roughly to genus, species, and variety in biology. 
3. It is believed, if once rock nomenclature be placed upon 
a reasonable basis, that this will be a great step toward the 
establishment of a satisfactory scheme of rock classification. 
4. Under the plan suggested it will be easy for the student 
