240 OUTLINES oi FIELD-GEOLOGY PAKMI 



it may be fastened to the end of a bobbin or other con 

 venient bit of wood by means of a rement formed of 

 three-parts of rosin and one of bees-wax, which is easily 

 softened by heating. A little prn< ti < will show that a 

 slow, equable motion with a certain steady pressure is 

 most effectual in producing the desired flatness of sir. 

 When all the roughnesses have been removed, w lu- 

 be told after the chip has been dipped in water so 

 remove the mud and emery, we place the specimen upon 

 the square of plate-glass, and with flour-emery and 

 continue to rub it down until all the scratches caused by 

 the coarse emery have been removed and a smooth 

 polished surface has been produced. Care should be 

 taken to wash the chip entirely free of any grains of coarse 

 emery before beginning to the polishing on glass. It is 

 desirable also to reserve the glass for polishing only. The 

 emery gets finer and finer the longer it is used, so that 

 by remaining on the plate it may be used many times in 

 succession. Of course the glass itself is worn down, but 

 by using alternately every portion of its surface and on 

 both sides, one plate may be made to last a considerable 

 time. If after drying and examining it carefully, we find 

 the surface of the chip to be polished and free from 

 scratches, we may advance to the next process. But it 

 will often happen that the surface is still finely scratched. 

 In this case we may place the chip upon the Water-of- 

 Ayr stone and with a little water gently rub it to and fro. 

 It should be held quite flat The Water-of-Ayr stone 

 too should not be allowed to get worn into a hollow, but 

 should be kept quite flat, otherwise we shall lose part 

 of the chip. Some soft rocks, however, will not take an 



