508 



Annals New York Academy of Sciences 



reported for New York City. Several of these objects are illustrated in figure 

 10. It is extremely difficult to prevent contamination by this type of ma- 

 terial. These types of particles are often present in great abundance in the 

 air and are deposited as dust that later forms a secondary source for con- 

 tamination. 



Siegel has pointed out in personal communication that he had found it 

 extremely difficult during the summer and fall to prepare Vaseline-coated 

 slides free of pollen contamination, although working in a dust free, "sterile" 



Figure 10. Objects found in pollen survey slides. (A) Unidentified object. (B) 

 Ragweed pollen grains. (C'j Oak pollen grain. (D) Unidentified object. The line is 20 n 

 in length. 



room. Also, ragweed pollen grains were occasionally seen by Siegel in pollen 

 study slides exposed long after the period of bloom, and probably represent 

 contamination from the laboratory or other sources. 



Thin Sedions 



Organized elements embedded in mineral veins in thin sections of the Orgueil 

 meteorite have been described and illustrated.- It is extremely important to 

 characterize these particles because they are undoubtedly indigenous to the 

 meteorite. However, the nature of the thin sections makes adecjuate morpho- 

 logical study difficult. The sections are relatively thick, 10 to 25 ^i, and al- 

 though the veins are composed of transparent minerals, there are irregularities 

 and impurities which cause optical distortion. It is difficult to be certain of 

 tine surface detail because the practical limit of resolution for the microscope 



