SPECIMEN-MOUNTING It was necessary to devise a special specimen- 



TECHNIQUES mounting technique in order to work with the 



small areas that are enlarged to full magnifica- 

 tions 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 individual wires. 



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

 eral ways: (1) manually, under high-power binoculars; (2) precipitated 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" 4 to 10" 5 milli- 

 meters of mercury in the electron microscope. However, the microscope 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 electron bombardment, and some materials may 

 heat up during this bombardment. Owing to the high vacuum, this heat cannot 

 be transmitted or conducted away from the subject. 



POSSIBLE USES IN The usefulness of any method of correlation 



CORRELATION WORK lies in its ability to indicate or prove the ex- 



istence of equitable or similar ages or environ- 

 ments of deposition between two areas, two wells, or two geologic outcrops. Most 

 methods in geology originally included only the megascopic aspects : for example, 

 similar or identical fossils and equivalent successions of beds, to mention two. 

 With the advances in geologic techniques, more precise correlation has been pos- 

 sible by utilizing microscopic similarities for correlations, as in micropaleontol- 

 ogy, 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 discussed. 



Bed Identification 



It is possible that many minute similarities exist in beds or formations, 

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

 beds. In studying sandstones, for example, it would not be possible to observe 

 the actual sand grains, but it would be necessary to study the cementing mate- 

 rial and any foreign material in the sandstone. 



144 



