66 H. J. (ri'djison : 



machine, though effective in his hands for his own purticuhir 

 Avork, is both crude and inconvenient for rock-section making. 



A machine of this character was sent from, London to the 

 Melbourne University some 10 years ago. It was said to be a 

 duplicate of one in use at the British Museum, and was 

 then regarded as an up-to-date machine for rock slicing. I 

 am unable to discover that this machine possesses any material 

 advantage over the older types of similar apparatus. 



Many years ago the late Mr. Jordan devised a siniple and 

 fairly convenient machine,^ worked by means of a treadle. 

 This machine, unlike that used by the lapidary, leaves both 

 hands free for other manipulations — which is a decided con- 

 venience. Ttis type of machine has since been modified, and 

 improved, in respect to details, more especially by German 

 petrologists, whose energies, however, seem to have been chiefly 

 directed to devising elaborate and ingenious clamps for hold- 

 ing and orientating the specimen to be cut. Nearly all the 

 more important German firms who cater for geologists now pro- 

 vide machines de.signed for driving either by foot or motor power. 

 Generally speaking also, German rock-slicing apparatus is dis- 

 tinctly in advance of that made by English and American firms. 



My reasons for building a machine, when so many other types 

 were available to choose from, were mainly as follows: — 



A fairly long experience in the preparation of rock sections 

 had served to bring out some of the weak points of at least 

 three machines with which I had worked. Moreover, I had 

 adopted a pi'ocess of section making, differing somewhat from 

 that ordinarily followed, which made it possible largely to 

 substitute slicing with diamond powder for grinding with 

 emery, without material increase in cost, and with a great 

 economy of time. 



One of the chief drawbacks pertaining to the machines of 

 which I hiid had experience, was that, ordinarily, they were 

 speeded to run at from :500 to 500 revolutions per minute. 



^ A plan and so(-tion of the Jordan machine may be found in KntU-y's "Study of 

 Rocks," p. 04, 4tli cd., 1S88. 



The ordinary lapidary's inachiiic is fiifured in Iloltzapffel's ■'.Mechanical Manipulation," 

 vol. iii., 1804 ed. 



