322 THE FOEAMINIFEEA 



balsam to a glass slide. The cover glass can then 

 be ground away or carefully flaked off, and the 

 rubbing down proceeded with until thin enough ; 

 it is then mounted in the usual way with Canada 

 balsam and a cover glass, great care being taken to 

 avoid displacing the prepared section by too much 

 pressure. 



It will now be convenient to describe the method 

 of making sections of chalk. 



The above plan will also answer equally well for this, 

 but the following is the usual way of procedure : — 



The chalk selected for the section should, if 

 possible, be cut into a slice with fairly parallel sides, 

 and having a thickness of ^ inch or so. This slicing 

 is not absolutely necessary, but it ensures the 

 better permeation of the rock ; whereas if a chip is 

 used it will take a longer period for the medium to 

 penetrate to the plane through which the section is 

 to be made. The slice or chip is carefully warmed, 

 to drive out any moist air which may lurk in the re- 

 cesses of the specimen ; and at the same time we 

 should have in preparation an evaporating basin, of 

 about 2^ inches in diameter, half filled with Canada 

 balsam, and resting on a tripod and piece of wire 

 gauze, placed over the flame of a spirit lamp. When 

 the balsam has been heated to the condition of being 

 nearly tough when cold, tested by drawing out 

 a thread on the point of the forceps, the piece of 

 chalk may be dropped in and allowed to absorb the 

 balsam freely. If a few flakes of shellac be added to 

 the balsam it will render the chalk more coherent 



