PALEONTOLOGY 1083 



methods in use for testing such particles micro-chemically. The 

 first is that proposed by Boricky, who employed pure hydro-fluo- 

 silicic acid (H 2 SiF 6 ), which attacks almost all rock-forming minerals. 

 The mineral particle is placed upon a glass object-holder protected 

 from the action of the acid by a covering of Canada balsam, and the 

 acid allowed to attack the mineral. After evaporation an examina- 

 tion under the microscope reveals the presence of delicate crystals 

 of the silico-fluorides of the metals present in the mineral. The 

 nature of the crystals may then be determined microscopically. 



The second method is that proposed by Behrens, and mostly 

 follows the usual method of chemical analysis. The isolated particle 

 is heated in a small platinum crucible with ammonium fluoride, the 

 mass then evaporated with sulphuric acid and dissolved in hot water. 

 A small quantity of the solution is then evaporated and examined. 

 If calcium is present in the mineral small crystals of gypsum will 

 form. Other quantities are treated w r ith the ordinary reagents. 

 The crystalline products, which are the result, can be identified by 

 optical methods. It is possible by Behrens's tests to detect the 

 presence of O0005 mgr. CaO in a grain. 



In all cases it is advisable to protect the objective during the 

 microscopical examination with a thin sheet of white mica. 



The microscope has always played an important part in the 

 science of Palaeontology. The great work on ' Micro-geology,' 

 published in 1855 by Professor Ehrenberg, testifies to the influence 

 it had, even at that period, upon research of this nature. 



The result of the microscopic examination of lignite or fossilised 

 wood and of ordinary coal is a good example of the value of the 

 instrument in this interesting department. Specimens of fossil 

 wood in a state of more or less complete preservation are found in 

 numerous strata of very different ages. Generally speaking, it is 

 only when the wood is found to have been penetrated by silica that 

 its organic structure is well preserved ; but instances occur every now 

 and then in which penetration by carbonate of lime has proved equally 

 favourable. In either case transparent sections are needed for the 

 full display of the organisation. Occasionally, however, it has hap- 

 pened that the infiltration has filled the cavities of the cells and 

 vessels, without consolidating their walls ; and as the latter have 

 undergone decay without being replaced by any cementing material, 

 the lignite, thus composed of the internal ' casts ' of the woody tissues, 

 is very friable, its fibres separating from each other like those of 

 asbestos ; and laminae split asunder with a knife, or isolated fibres 

 separated by rubbing down between the fingers, exhibit the characters 

 of the woody structure extremely well when mounted in Canada 

 balsam. Generally speaking, the lignites of the Tertiary strata 

 present a tolerably close resemblance to the woods of the existing 

 period : thus the ordinary structure of dicotyledonous and monocotyle- 

 donous stems may be discovered in such lignites in the utmost 

 perfection ; and the peculiar modification presented by coniferous 

 wood is also most distinctly exhibited. As we go back, however, 

 through the strata to the Secondary period, we more and more rarely 

 meet with the ordinary dicotyledonous structure ; and the lignites of 



