24 Ofii.iM SOI in LD-GBOLO 



The hammer han^s .it the lelt 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-pocket- 

 carry the hammer tl 



3. The Lens. Even the most sharp-sighted observer 

 is the better of the aid supplied to him by a good mag- 

 nify ing -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 striae on a crystal, and the 

 minuter ornament on the surface of a fish-scale or other 

 fossil organism. A platyscopic lens, combining the ad- 

 vantages of a wide field with strong magnifying power is 

 a most useful instrument. Applied to the weathered 

 crust of a rock, a lens often enables the observer to de- 

 tect 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 coloured on the 

 map. 



4. The Compass. 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. 

 This is the instrument employed in the Geological Sur 



