84 THE MICROSCOPIST. 



CHAPTER VII. 



THE MICROSCOPE IN MINERALOGY AND GEOLOGY. 



MICROSCOPIC examination of minute fossil organisms, as 

 Diatoms, Foraminifera, spicules of sponge, etc., has long 

 been a subject of interest. Latterly, however, the micro- 

 scope has been found to be essential to the study of phys- 

 ical geology and petrology. How many crude and verbose 

 theories respecting cosmogony will disappear by this means 

 of investigation time must reveal, but the animal nature 

 of the Eozoon Canadense found in the Serpentine Lime- 

 stone of the Lauren tian formation of Canada, parallel with 

 the Fundamental Gneiss of Europe, and the discovery by 

 Mr. Sorby* of minute cavities filled with fluid in quartz 

 and volcanic rocks, are indications that speculations based 

 upon a merely external or even chemical examination of 

 rock structures are immature and inadequate. 



The systematic study of microscopic mineralogy and 

 geology will require a large outlay of time and patience, 

 and the field is one which is scarcely trodden. The plan 

 of this work will only permit a brief outline, sufficient to 

 aid a beginner, and indicating the value and the methods 

 of minute investigation. 



Preparation of Specimens. Examination of the outer 

 surface of a mineral specimen, viewed as an opaque body 

 with a low power and by condensed light, is sometimes 

 useful. The metals and their alloys, with most of their 

 combinations with sulphur, etc , admit of no other method. 

 Occasionally, as in iron and steel, the microscopic structure 

 is best seen by polishing the surface, and then allowing 

 the action of very dilute nitric acid. Mr. Forbesf states 



* See Beale's How to Work with the Microscope. 



f The Microscope in Geology, Popular Science Keview, No. 25. 



