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ABSTRACT

A significant recent advance in microscopy has been the introduction of differential-interference contrast (DIC) optics. In reflected-light instruments, one “Nomarski prism” (a modified Wollaston prism) is used both for beam splitting and combining. In effect, two deformed wave-fronts are produced which are laterally separated by a distance below the resolving power of the microscope. They are brought to differential interference by the analyzer, the effect being one of oblique illumination of the object.

This system can be used in the study of mineral-grain surfaces. For this purpose, conventional replicas of the grains are placed on petrographic slides which in turn are placed over a silvered mirror on the microscope stage. The Nomarski prism is then adjusted until the best contrast is achieved.

For a test study, samples were collected from the intertidal zone of the Atlantic shore of eastern Long Island, mostly at localities which earlier were sampled by Krinsley et al. (1964) and studied in a classical investigation of quartz-grain surface features by transmission electron microscopy. In the present study, a semi-quantitative evaluation of surface features was attempted, using as guide the criteria set up by Krinsley and his school. The results of this study are tentatively interpreted as reflecting pronounced erosion in the study area, and increasing energy levels from East Hampton to Montauk Point.