

GEOLOGICAL SURVEYING 275 
To these it is well to add a small protected bottle of dilute 
hydrochloric acid, and, of course, a pocket-knife. 
The Hammer.—I\n the selection of a hammer tastes differ. 
For general purposes, however, that used by the officers of 
the Geological Survey can hardly be surpassed.* It should 
not weigh much over one pound—unless the observer expects 
to be working principally among hard and tough rocks, such 
as granite, gneiss, and schists, when it may be desirable to 
have a somewhat heavier implement. The student will soon 
learn, however, that there is a certain art even in breaking 
stones. An adept by one dextrous blow with a light hammer 
will often strike off a “specimen” from some hard, tough 
_rock, which a tyro armed with a much heavier tool may 
vainly assail—all his efforts resulting only in the production 
of so much grit and powder. There is some art not only in © 
the elastic swing of the arm as the blow is delivered, but in 
the selection of the spot to be struck, which will be determined 
partly by the shape of the rock-surface and partly by the 
nature of the rock itself. 
If the geologist wishes to collect rock-specimens as he 
goes along, a heavier hammer will be necessary to detach 
fragments of a sufficient size, besides which a much smaller 
tool will be required to trim the specimens to the desired 
size and shape. To these some geologists add one or more 
chisels, such as are used by masons. ‘These additional 
impedimenta may be carried in the strong moleskin bag 
required to hold his rock-specimens and fossils. Heavily 
burdened in this way, however, the progress of the hammerer 
is apt to be impeded; and if his chief object be mapping, he 
will do well to leave specimen-collecting alone until his 
survey is completed. After his map is finished, he can devote 
a few days to gathering such specimens as he wishes to 
procure. As geological surveying often involves climbing in 
ticklish places, and much hard walking over rough ground, it 
is well to go as lightly as one can, if rapid progress be desired. 
A few capacious pockets to hold the small specimens and 
chips one may wish to examine carefully at home, will be 
found more convenient than a bag—the temptation to fill 
* This hammer is introduced into many of the Plates illustrating this 
book, see especially Plates X., XXXII., XLIX. 

