purely geological purposes. On steep, grassy slopes, where the footing is precarious, and where there is no available hold for the hand, the wedge-like end of the hammer may be driven firmly into the turf, and the geologist may thereby let himself securely down or pull himself up.
The most generally convenient way of carrying the hammer is to have it in a leather sheath suspended from a waist-belt. The hammer hangs at the left side under the coat, the inside of which is kept from being cut or soiled by the protecting outer flap of the sheath. Some geologists prefer to carry the belt across the shoulders outside, and the hammer suspended at the back. Others provide themselves with strong canvas coat-pockets and carry the hammer there.
Even the most sharp-sighted observer is the better for the aid supplied to him by a good magnifying-glass. For field-work a pocket lens with two powers is usually sufficient. One glass should have a large field for showing the general texture of a rock, its component grains or crystals, and the manner of their arrangement; the other glass should be capable of making visible the fine striæ on a crystal, and the minute ornament on the surface of a fish-scale or other fossil organism. Applied to the weathered crust of a rock, the lens often enables the observer to detect indications of composition and texture which the fresh fracture of the rock does not reveal. It sometimes suffices to decide whether a puzzling fine-grained rock should be referred to the igneous or the aqueous series, and consequently how that rock is to be colored on the map.
Any ordinary pocket-compass will suffice for most of the requirements of the field-geologist. Should he need to take accurate bearings, however, a small portable azimuth compass will be found useful.