2 ;s OUTLINES OF FIELD-GEOU 



of the rock, the rule being to make the slice as thin as 

 the rock will allow, so as to save labour in grinding down 

 afterwards. 



ellent rock-sections, however, may be prepared 

 without any machine, provided the operator possesses 

 ordinary neatness of hand and patience. He must pro- 

 cure as thin chips as possible of the rocks he proposes 

 to slice. These he can usually obtain in the field where 

 he is hammering. He should select as fresh a portion 

 of the rock as may be accessible, and by a dexterous 

 use of the hammer break off from a sharp edge a number 

 of thin splinters or chips, out of which he can choose 

 one or more for making into rock-slices. These (hips 

 may be about an inch square. It is well to take several 

 of them, as the first specimen may chance to be spoiled 

 in the preparation. The geologist ought also always to 

 carry off a piece of the same block from which his chip 

 is taken, that he may have a specimen of the rock for 

 future reference and comparison. Every such hand- 

 specimen, as well as the chips belonging to it, ought to 

 be wrapped up in paper on the spot where it is obtained, 

 and inside the wrapper or affixed to the specimen, there 

 should be a label or piece of paper with the locality and 

 any notes that may be thought necessary. It can hardly 

 be too frequently reiterated that all such field- notes 

 ought as far as possible to be written down on the ground 

 where the actual facts are before us for examination. 



Having obtained his thin slices, either by having 

 them slit with a machine or by detaching with a hammer 

 as thin splinters as possible, the operator may proceed 

 to the preparation of them for the microscope. For this 



