Subsurface Laboratory Methods 205 



exposing a photographic plate to the electrons. This plate is carried in a 

 holder in the vacuum system of the microscope. Magnifications of 1,000 

 to 20,000 diameters are possible, and the definition of the photograph is 

 sujfficiently clear to allow further optical enlargement to full useful mag- 

 nification. 



Specimen-Mounting Techniques 



It was necessary to devise a special specimen-mounting technique in 

 order to work with the small areas that are enlarged to full magnifications 

 for study. Most specimens are mounted on a 400-mesh screen. This screen 

 is dipped into a solution of collodion, which dries quickly, leaving a 

 strong film approximately one micron (0.001 mm.) thick between the in- 

 dividual wires. 



The material for study may be placed on this collodion film in one of 

 several ways: (1) manually, under high-power binoculars; (2) precipi- 

 tated from solution onto the screen; (3) by passing the screen coated 

 with collodion through a culture of the material; and (4) by placing a 

 drop of material suspended in a liquid onto the screen. 



No wet or living tissue can withstand the high vacuum of 10"* to 10'^ 

 millimeters of mercury in the electron microscope. However, the micro- 

 scope is being used extensively in biological studies on materials ranging 

 in size from that of the organs of animals and insects downward through 

 that of the bacteria and of the viruses and even of large molecules. The 

 material in turn must be thin enough to allow the passage of electrons 

 through it. Some materials deteriorate when subjected to the intense elec- 

 tron bombardment, and some materials may heat up during this bombard- 

 ment. Owing to the high vacuum, this heat cannot be transmitted or con- 

 ducted away from the subject. 



Possible Uses in Correlation Work 



The usefulness of any method of correlation lies in its ability to 

 indicate or prove the existence of equitable or similar ages or environ- 

 ments of deposition between two areas, two wells, or two geologic out- 

 crops. Most methods in geology originally included only the megascopic 

 aspects: for example, similar or identical fossils and equivalent succes- 

 sions of beds, to mention two. With the advances in geologic techniques, 

 more precise correlation has been possible by utilizing microscopic sim- 

 ilarities for correlations, as in micropaleontology, sedimentary petrology, 

 and microlithology. 



With the electron microscope, it should be possible to achieve the 

 ultimate in utilizing submicroscopic similarities for correlations. Some 

 uses possibly peculiar to this microscope are herein listed and discussed. 



Bed Identification 



It is possible that many minute similarities exist in beds or forma- 

 tions, which, if they could be seen and studied, could be used to correlate 



