EXAIMINATION OF STRUCTURE OF FOSSIL PLANTS. 17 



In operating on siliceous objects, I have found soap and 

 water quite as speedy and efficacious as oil, which is generally 

 used ; while calcareous fossils must be slit by a solution of 

 common soda in water. This solution of soda, if made too 

 strong, softens the india-rubber on the face of the pneumatic 

 chuck, and renders a new piece necessary; but if care is 

 taken to keep the solution of moderate strength, one piece of 

 india-rubber may last for six months. The thinner and 

 flatter it becomes, the better hold the glass takes, until a 

 puncture occurs in the outer portion, and a new piece is 

 rendered necessary. 



The polishing of the section is the last operation. This is 

 performed in various ways, according to the material of which 

 the organism is composed. If siliceous, a lap of tin is to be 

 used, about the same size as the grinding lap. Having turned 

 the face smooth and flat, a series of very fine notches are to 

 be made all over the surface. This operation is accomplished 

 by holding the edge of an old dinner-knife almost perpendi- 

 cular to the surface of the lap while rotating ; this produces 

 a series of cridcUes, or slight asperities, which detain the 

 polishing substance. The polishing substance used on the 

 tin lap is technically called lapidaries' rot-stone, and is 

 applied by slightly moistening the mass, and pressing it firmly 

 against the polisher, care being taken to scrape off the outer 

 surface, which often contains grit. The specimen is then to 

 be pressed w4th some degree of force against the revolving' 

 tin lap or polisher, carefully changing the plane of action, by 

 moving the specimen in various directions over the surface. 



To polish calcareous objects, another method must be 

 adopted as follows : — 



A lap or disc of willoAV wood is to be adapted to the 

 spindle of the lathe, three inches in thickness, and about the 

 diameter of the other laps (10 inches), the axis of the wood 

 being parallel to the spindle of the lathe, that is, the acting 



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