Rock Section Cutting Apparatus. 79 



[lowder. there should l)e no seoriuu' or scratches ; the latter, if 

 present, beinir due to fragments of too coarse a powder, or to 

 its use in too limited a quantity, thus allowing the specimen 

 to come in contact with the metal of the lap. As a rule, and 

 for safety, it is wiser to ^ive the last touches by hand upon 

 a suitable lap of slate or glass, using only the finest washed 

 powder. 



The whole process is not so long, or so complicated as any 

 description must necessarily seem to imply. With the aid of 

 the machine described, and given balsamed slides in readiness, 

 I find it possible to complete single slides in 10 to 15 minutes : 

 the finished section, in area, uniformity and thinness, leaving 

 little to be desired. Furthermore, with a series of rocks — and 

 it is usual to treat a number together — there is a correspond- 

 ing gain in time, throughout the several operations. Xaturally 

 too, and perhai)s more particularly with the type of machine 

 just described, individual experience, dexterity of manipulation 

 and judgment, are material factors affecting the final result, 

 both as to time and quality of work. Compared with the older 

 type of machine, both hand and treadle, there can be no ques- 

 tion as to the net gain, in time and labour, both of which are 

 important. There is, too, I think, an equivalent improvement 

 in the average quality of the finished product. On these 

 grounds I hope the publication of this brief desci'iption will 

 prove useful to all who are interested in the preparation of 

 rock sections. 



EXPLANATION OF PLAJES XIV.-XVIl. 



Plate XIV. 



New Rock-Slicing Machine, Melbourne University. Side 

 view, showing slicing disc and grinding laps, and the supporting 

 rods for the various clamps and specimen holders. The levers 

 which operate the driving mechanism can be seen above and 

 somewhat behind the spindles. The guard trays have been 

 removed, so as to show the several parts of the machine more 

 clearly. The lathe in the foreground is independent of the rock 

 machine. 



