314 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1957 



a grain size coarser than that of fine sand facilitate the penetration of 

 oxygen and percolation of ground water to an extent destructive to 

 spores and pollen. 



Sedimentary rocks altered by the heat and pressure of metamorphism 

 or by extensive weathering and exposure are usually sterile, although 

 they may once have contained pollen. Original sterility may be the 

 case in deep-water deposits which were laid down too far from land to 

 receive an appreciable pollen rain. 



The preparation of fossil pollen requires the facilities of a chemical 

 laboratory equipped with a fume hood, centrifuge, miscellaneous 

 glassware, and a microscope providing magnifications between 100 

 and 1,200. Care must be taken to prevent the introduction into the 

 sample of stray pollen from dirty glassware or the air. 



Pollen and spores imbedded in a sediment must be separated from 

 the mineral matrix in order to observe them. Detailed explanations 

 of the treatments used are given by Faegri and Iversen (1950) . Two 

 common procedures employed to accomplish the separation entail 

 either dissolving the mineral fraction by reagents that will not destroy 

 pollen, or differential flotation of the sediment using heavy liquids 

 in which the organic residues float while the mineral fraction sinks. 

 Common reagents for the first procedure are HC1 for dissolution of 

 carbonates, followed by HF to eliminate silicates. The second (flota- 

 tion) technique may be accomplished, after physical maceration of 

 the rock, by the use of a bromoform-acetone mixture adjusted to a 

 specific gravity of 2.3 (Frey, 1954). Coals may be broken down by 

 oxidation with Schulze's solution. The high concentration of dark 

 humic substances in coal, lignite, and peat often requires the use of 

 decolorizing agents, bleaches or strong bases, to clarify the otherwise 

 opaque organic material. Acetylation is often used to remove cellu- 

 lose. Variations of these procedures have been developed in each 

 pollen laboratory to deal with the matrix at hand. 



After the pollen is isolated from the sedimentary matrix, it is washed 

 free of the reagents used in preparation and mounted on slides in 

 glycerine jelly, balsam, or a synthetic mounting medium. 



INTERPRETATION OF THE FOSSIL SAMPLE 



Because of the similarity of Pleistocene plants to modern ones, 

 identification of their pollen with modern genera or (in part) species 

 is theoretically possible for such relatively young material. Much 

 pollen of Tertiary age can safely be attributed to living genera too, 

 but in Cretaceous assemblages the detection of modern genera is usually 

 difficult and often questionable because of the great amount of evolu- 

 tion and extinction that has since occurred. Older fossil material, e. g., 

 pre-Cretaceous spores and conifer pollen, is usually placed in extinct 



