PALEOBOTANICAL MICROTECHNIQUE 155 



used in sawing wood, but is a plain band of metal which must not be 

 too hard. To be ideal, it should have diamond dust driven into the 

 margin; but, since the expense would be considerable, carborundum 

 powder and water can be used instead. A band saw is a dangerous 

 piece of apparatus and the operator should be thoroughly protected 

 from a broken, whipping saw. 



2. The cut surface can be polished on a revolving brass plate, kept 

 wet, and liberally powdered with fine carborundum. 



Or, the cut surface can be rubbed by hand on a piece of plate glass, 

 with plenty of carborundum. This is a more rapid method and most 

 investigators prefer it. When the surface has become even and smooth 

 the specimen is ready for the next step. 



3. Fasten the polished surface to the glass slide upon which the sec- 

 tion is to be mounted. Plate glass 3 or 4 mm. thick is best for sections 

 larger than 3 or 4 cm. square. Gradually heat the slide until it is 

 quite hot. Melt upon the slide the thin flakes of white shellac used by 

 painters; heat the object and press the polished surface very firmly into 

 the melted shellac. Canada balsam, from which the xylol has been 

 driven off by heating, can be used instead of shellac. Much of the 

 Paleozoic material is in the form of coal balls. After the ball has been 

 cut in two, it is often difficult to hold the hemispherical piece in a 

 clamp, especially if the piece is small. In such cases, it is better to 

 fasten the polished surface to a convenient .piece of marble, about 2.5 

 cm. thick, and 5 or 6 cm. square. The marble is easily held in the 

 clamp. As soon as the slide, or marble, and object are cool, the next 

 cut can be made. 



4. Fasten the object in the clamp and saw as close to the glass, or 

 marble, as possible, thus leaving a thin section cemented to the slide 

 or marble. If marble has been used, the section is removed by heating 

 or by dissolving it off with xylol. It can then be fastened to the glass 

 slide for grinding and polishing. Anyone who can handle tools should 

 soon be able to cut a section 1 mm. thick. A skilled technician can cut 

 sections as thin as 0.5 mm. 



5. The second grinding must be very careful and accurate. This 

 can be done on the revolving brass disc; but here, again, a piece of 

 plate glass, with plenty of carborundum, and water, is gaining favor 

 over the more expensive revolving disc. The glass slide allows one to 

 note how the process is progressing. 



