7 io THE POPULAR SCIENCE MONTHLY. 



purely geological purposes. On steep, grassy slopes, where the foot- 

 ing 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. 



Fig. 1. Geological Hammer, Compass-Case, and Belt. 



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 sup- 

 plied 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 fisld 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 striae 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 re- 

 ferred 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 require- 

 ments of the field-geologist. Should he need to take accurate bear- 

 ings, however, a small portable azimuth compass will be found useful. 



