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The AAPG/Datapages Combined Publications Database
With the advent of the scanning electron microscope (SEM) a new dimension was opened to the micropaleontologist. At its maximum useful magnification of 50,000 diameters, the SEM offers a depth of field of about 10 µ and a resolution of about 200 A, whereas the optical light microscope, at its maximum useful magnification of 1,300 diameters, offers a depth of field of about 0.5 µ and a resolution of about 2,00 A. Inasmuch as the classification of diatoms and silicoflagellates is based on the general and detailed characters observed with the light microscope, the use of the SEM must be viewed as an extension of the facilities offered by the light microscope. Ten species of diatoms and silicoflagellates from Miocene rocks, exposed at Newport Beach, California, have been studied with the light microscope and the scanning electron microscope. A comparison of the micrographs of the identical species taken with the two instruments clearly demonstrates the ability of the SEM to provide a more detailed description of taxa, a more precise circumscription of taxa, a separation of closely allied taxa, and a verification of many varieties of taxa.
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