J. B. JORDAN ON ROCK SECTIONS. 189 



until all traces of the lines of grinding and scratches are 

 removed. 



Having thus obtained a perfect section on the plate glass, it is 

 easily removed, by gently heating over a spirit lamp, and should be 

 placed in spirits of turpentine for an hour or two to dissolve oif all 

 superfluous balsam. In order to ensure a perfectly clean section 

 it is well to boil it in fresh turpentine before mounting. 



Thin sections of rocks are usually mounted in Canada balsam 

 under a glass cover in the ordinary way. 



On the reading of this paper a series of specimens was exhibited, 

 shewing the various stages in the operation of preparing rock 

 sections for Microscopical Examination. 



