
‘Parr Il, § vii] DETERMINATION OF ROCKS. 17. 
a 
Seek 5 
possible the locality from which it was taken. This information 
_ ought always to be written down in the field at the time of collecting, 
_ and should be wrapped up with the specimen, before it is consigned 
~ 
to the collecting bag. If, however, the student does not purpose to 
form a collection, but merely to obtain such chips as will enable him 
to judge of the characters of rocks, a hammer weighing from 14 to 
2 lbs. and of the shape indicated in Fig. 31 will be sufficient. The 


' Fic. 31.—Hammer, SHeatu, AND BELT, WITH LEATHER-CASE FOR HOLDING 
AzimuTH CoMPAss. 
advantage of this form is that the hammer can be used not only for 
breaking hard stones, but also for splitting open shales and other 
fissile rocks, so that it unites the uses of hammer and chisel. 
It is of course desirable that the learner should first acquire some 
knowledge of the nomenclature of rocks, by carefully studying a 
collection of correctly named and judiciously selected rock-specimens. 
Such collections may now be purchased at small.cost from mineral 
dealers, or may be studied in the museums of most towns. Having 
accustomed his eye to the ordinary external characters of roeks, and 
become familiar with their names, he may proceed to determine them 
for himself in the field. 
Finding himself face to faee with a rock-mass, and after noting 
its geotectonic characters (Book IY.), the observer will proceed to 
examine the exposed or weathered surface. The earliest lesson he 
has to learn, and that of which perhaps he will in after life meet 
with the most varied illustrations, is the extent to which weathering 
conceals the true aspect of rocks. From what has been said in 
y 
d 
. 
~ 
previous pages, the nature of the alterations will be understood, and 
further information regarding the ehemical processes at work will 
be found in Book III. The practical study of rocks in the field soon 
N 
