THE STUDY OF ROCKS. 
11 
minutes nothing was said by either of us. I watched him close¬ 
ly as he seemed to be meditating. Suddenly he looked up, 
stroked his beard, and declared, with the air and in a tone of 
thorough conviction, that “ Something or other must have done 
that.” After such a manifestation of interest I could not for¬ 
bear to give the old gentleman some elementary information in 
regard to glaciers and the work they have done as geological 
agents. I never had a more attentive or interesting audience 
in my life. As I boarded the train my audience thanked me 
for the lesson and declared that he should look upon rocks 
with a different feeling thereafter. 
There is no question but that there are many who need only 
a few suggestions or directions in order to get started in a 
proper manner for a satisfactory study of the rocks. The num¬ 
ber of common minerals does not exceed fifty, and some of these 
have such prominent characteristics that a few simple tests dis¬ 
close their identity. There is still a larger number, not so 
easy of identification, but concerning which it is comparatively 
easy to obtian a clew. Then, following up the clew by use of 
properly prepared tables and apparatus discloses the family 
name and, in most cases, the species. For example, the lack of 
cleavage, its vitreous lustre, and hardness will in most cases 
distinguish the common varieties of quartz, the most widely 
distributed mineral with a single exception. The peculiarities 
of coloration of the less common varieties of quartz, in addi¬ 
tion to the other properties, will generally suffice to distinguish 
these also. 
Take also mica, a very widely distributed mineral in New 
England, and specially prominent in New Hampshire. After 
an examination of its tructure, even a brief one, the thin leaves, 
or foliae, are so prominent, that no one wonders that it is cited 
as the type of perfect cleavage ; and its structure in thin sheets 
is so pronounced that when another mineral is found that re¬ 
sembles it in this particular it gives the name to the structure, 
i. e., micaceous. 
There is another mineral, or rather, family of minerals, the 
