Fossil Vegetables. Ill 



It may be valuable to the geologist who wishes to examine fossils 

 by the microscope, to have a formula of Mr. Witham's mode of pre- 

 paring the specimens, for which he acknowledges himself indebted 

 10 Mr. Nicqll. 



He first cuts a thin slice from the fossil wood, in a direction per- 

 pendicular to the length of its fibres. The slice thus obtained must 

 be ground perfectly flat and then polished. The polished surface is 

 to be cemented to a piece of plate, or mirror or glass a little larger 

 than itself, by means of a thin layer of Canada Balsam, applied to 

 the polrshed surface of the slice, and also to one side of the glass. 

 The slice and the glass must now be laid on a common fire shovel, 

 and gradually heated over a slow fire, to concentrate the balsam. It 

 will require great care to prevent the heat from becoming so great 

 as to throw the balsam into a state of ebullition, for if air bubbles are 

 formed in it, it will be difficult to remove them and they will prevent 

 the complete adhesion of the two surfaces, when applied to each 

 other. The heat of the shovel should never become so great that 

 the fingers may not be held against it without inconvenience. With 

 every precaution, some few bubbles will sometimes make their ap- 

 pearance, but these may be removed by a small stick tapering to a 

 fine point. When the balsam is sufficiently concentrated, and the air 

 bubbles removed, the slice and the glass may be taken from the 

 shovel, and applied to each other. A slight degree of pressure will 

 be necessary to expel the superabundant balsam, and this will be fa- 

 cilitated by gently sliding the one on the other. By this kind of mo- 

 tion, any air which might have got entangled in the balsam will also 

 be removed. 



When the whole is cooled to the temperature of the air, and the 

 balsam has become solid, that part of it which adheres to the glass 

 surrounding the slice, should be removed by the point of a pen knife, 

 and by this operation, it will be seen whether the balsam is properly 

 concentrated. If it has entirely lost its sectility, and starts oiFin' 

 flakes before the knife, it will be found that the slice and glass cohere' 

 so firmly, that in the subsequent grinding, there will be no risk of their 

 separation. If the balsam is not sufficiently concentrated, it will slide 

 before the knife, and the two bodies will not adhere with sufficient 

 firmness. If the layer of balsam be not too thick, its due concentra- 

 tion may be accomplished in four or five minutes. 



The slice must now be ground down to that degree of thinness 

 which will permit its structure to be seen by the microscope. The 



