32 OUTLINES OF HELD-GI PART i 



with the whole box being easily portable. The i 

 will find a list of the more essential articles in Chapter 

 XVI. By means of the blow-pipe it is often possible to 

 determine the nature of a doubtful mineral or rock, and 

 to ascertain the proportion of metal in an ore. A young 

 geologist should begin by taking with him to the field 

 only the most essential apparatus and re-agents; hi- will 

 gradually come to see by practice what additions he may 

 best make to his equipment Details on this subject will 

 be found in Chapter XVI. 



8. Rock-slicing Apparatus. Portable forms of slicing 

 and polishing machines are now to be procured, though 

 even the lightest of them add considerably to the travrlk r's 

 baggage. The field-geologist may succeed, however, in 

 preparing his slices by chipping thin splinters from the 

 rock and reducing them in the manner described in 

 Chapter XVII, where instructions are given which it is 

 hoped will enable him to supply himself with a micro- 

 scopic slice of any rock he may encounter in the field. 

 The labour involved in this process is well bestowed, for 

 by means of the microscope, more than by any other 

 method, he obtains an insight into the internal texture 

 and arrangement of the rocks with which he is dealing. 

 He sees what are the component minerals of a rock, and 

 how they are built up to form the mass in which they 

 occur. He likewise can detect many of the changes which 

 these minerals have undergone, and he thus obtains a 

 clue into some of the metamorphic processes by which 

 the rocks of the earth's crust have been altered. 



9. Microscope. This instrument should be, like the 

 rest, as portable as possible. For most purposes of field- 



