GEULOGY. 181 
scientific observer has to depend more on his own knowledge and 
faculty for observation, and less on instrumental appliances, than a 
geologist. 
The best hammer for general purposes should weigh from 12 to 
24 oz. and should have a square flat end, and a straight cutting end 
—the latter may be horizontal or vertical, according to fancy. The 
ends should be of steel, not too highly tempered. The hole for the 
handle should be as large as possible (with a small hole the handles 
are so weak as to be liable to break), and the handle should be 
secured in the hole by a wooden wedge, and an iron one driven into 
and across the wooden one. It is advisable to take a few spare 
ash handles. It is as well to have more than one hammer in case 
of loss; and for fossil collecting, at least one heavy hammer with one 
end fashioned to serve as a pick, three or four cold chisels of various 
sizes, and a short crowbar will be found useful. 
A very good pocket compass is made in the shape and size of a 
watch with a clinometer arm. The use of the clinometer is for 
measuring the angle of dip in rocks. In an uneven country it is not 
easy without the clinometer to judge which is the line of greatest 
inclination of a stratum; and it is always more satisfactory to 
observe the angle than to estimate it. A flat piece of rock repre- 
senting the general slope can usually be found, and by placing a 
note-book on it the measurement can be facilitated. It is best to 
determine and record the “ strike”—that is, the direction of a hori- 
zontal line on the surface of the stratum—first; then at right angles 
to this line measure the “dip,” or angle of inclination, and note its 
direction by compass, correcting for variation. The lie of a bed is 
fixed if the direction and amount of the dip be recorded—the strike 
being always at right angles to the dip. Ina country where slaty 
cleavage occurs, precautions are needed, which will be noticed as we 
proceed. As a rule, except with very low angles of dip, the variation 
in the inclination of the rocks themselves exceeds tiie limits of error 
of the instrument. A little care, however, is necessary in taking dips ; 
for the apparent dip seen in a section, such as is often exposed in a cliff, 
may differ widely from the true dip, which will only be shown if the 
section runs at right angles to the strike of the beds. Dips seen on 
the sides of hills at a distance are but rarely correct, for the same 
Teason. 
A prismatic compass and an aneroid are frequently of great 
service: the former to determine the position on the map, if one 
exists, and to aid in making a rough map, if there be none; and the 
latter to estimate roughly the heights on the road travelled, especially 
