Recent and Fossil Coni/er<F. 157 



claim to the latter than I have. It was first employed in this 

 quarter by Mr Sanderson, the lapidary *. 



The manner in which he (Mr Sanderson) prepared his sections 

 was attended both with difficulty and uncertainty, and was inap- 

 plicable to the making of large sections of fragile fossils. He first 

 ground a surface flat, and then with lapidary's cement fixed that 

 surface to a block of wood. The fossil was afterwards ground 

 down until it was thought thin enough. When that was done it 

 was difficult to detach it from the block and remove the cement 

 without breaking it ; and whether too thick or too thin, it must 

 remain as it was, it being impossible to alter it. WTieii I first 

 began to prepare such sections, I had recourse to a process I had 

 practised upwards of fifteen years ago, in preparing thin slices of 

 the most fragile substances, as calcareous spar, in order to exa- 

 mine their effects on polarised light. My process was simple and 

 of easy execution, and consisted of cementing with duly concentrate 

 ed Canada balsam, the fiatteried surface to apiece of plate glass ^ 

 and then giinding down with emery on a plate of copper. The 

 glass and cement being both transparent, I could, zmtli cer- 

 tainty, determine when I had arrived at the proper degree of 

 thinness, and, when that was attained, nothing more was requi- 

 site than to polish the surface. At Mr Witham^s request, I wrote 

 a full account of all the manipidations requisite in my method 

 of preparing thin fossil sections, which is printed towards the 

 end of that gentleman'' s work. 



Explanation of Plates- 



Plate II. 

 Fig. L Transverse section of Pinus strohus. a. Annual layers. 



2. Longitudinal section parallel to a radius. 



3. Longitudinal section concentric. 



4. Transverse section of Taxus baccata, a. Annual layer. 



5. Longitudinal section parallel to a radius. 



6. Longitudinal section concentric. 



• This mode of shewing the structure of fossil woods has been long known ; 

 and for years I have been in the practice of recommending it to the atten- 

 tion of geologists. — Edit. 



