208 Subsurface Geologic Methods 



abundance of masses of minute fibers. These fibers are the so-called micro- 

 crystalline masses that cannot be identified or resolved under the polar- 

 izing microscope. 



Infusorial earth is described as a "siliceous earth made up largely of 

 siliceous fragments of Infusoria, used as fulling material and as a filter- 

 ing and absorbing agent." Figure 88 is an electron-microscope picture of 

 this material, X 20,000, showing fibers very similar to the Attapulgus clay. 

 The similar shapes of constituent parts of these two materials attest to their 

 similar physical properties. 



Clays might lend themselves to study and correlation in the electron 

 microscope in the following ways: 



1. The submicroscopic mineralogy and crystallography of clays 

 might be studied. Minute crystals of rutile have been identified in titanium- 

 rich clays. These crystals were too small to be identified under a light 

 microscope. Detailed studies should bring out several similar instances 

 of submicroscopic mineralogy that could be of value in correlation. 



2. The presence of submicroscopic organic forms too small to be 

 identified or even noted under a light microscope could provide the 

 means for bed identification. This would involve the development of, 

 shall we say, "electron micropaleontology," wherein organic forms far 

 below the smallest fossil known would be studied, 



3. Structural details of clays, pertaining to possible physical and 

 physicochemical properties of the clays, should lend themselves to study 

 in the electron microscope. The importance of this point might be stressed 

 by suggesting that the electron microscope is believed to be capable of 

 resolving giant molecules. At these particle sizes the physical and chem- 

 ical properties would be dependent one upon the other and should be diffi- 

 cult to separate. 



4. In the same general way, clay residues from limestones might be 

 studied. Identification would depend upon the structural details and per- 

 haps the mineralogy. Chemical or spectrographic methods of study would 

 probably be of more value here than would the electron microscope. 



5. Physical studies of the response of clays to the high vacuum in 

 the electron microscope and changes due to the electron bombardment, 

 with subsequent heating of the samples, might yield significant similari- 

 ties and diff'erences of correlative value. 



Long-Range Correlation 



The foregoing discussion has involved detailed correlations between 

 individual beds. It was pointed out that electron-microscope techniques 

 are not in general use as yet and may not be used except in unusual cases. 

 Long-range correlations, of course, depend upon equivalent criteria being 

 found over long distances. For this reason, long-range correlations with 

 the electron microscope are subject to the same considerations as were the 

 closer, detailed correlations. 



