the end of the tray. The fine fraction will be on the bottom and the coarse 

 pieces on top. Now reverse the tilt of the tray and knock it sharply a few times. 

 The coarse pieces will roll toward the other end, leaving a trail of the fines 

 behind. Much or all of this coarse material may be cavings, and the fine chips 

 are now segregated for examination. This process of segregating the coarse 

 and fine fractions requires but a few seconds. 



Samples are sometimes contaminated with steel shavings off the drill bit. 

 In some instances the steel shavings may constitute a substantial proportion of 

 the sample, making it difficult to study the cuttings. To remove the shavings, 

 first place a sheet of paper over the cuttings, which have been spread evenly 

 in the tray, and then pass a small magnet over the paper. The shavings will 

 cling tightly to the under side of the paper. Lift the paper and magnet together 

 as a unit to remove the shavings. When the magnet is lifted, the shavings fall 

 and leave the magnet clean. 



When samples are improperly washed, very fine clays, powdered limestone, 

 or dried drilling mud forms a fine dust which adheres tightly to the chips. It 

 is impossible to make a reliable determination of samples in this condition. It 

 may be necessary to rewash the samples, but as a rule washing facilities are not 

 available. The next best thing to do is winnow the sample in front of an electric 

 fan. Make a cursory examination of the cuttings to ascertain that there is no 

 essential fine fraction that might be lost. Place the fan on a large piece of paper, 

 such as a newspaper. Now rub the sample between the palms of the hands 

 directly in front of the fan, allowing the chips to fall slowly through the air 

 stream to the paper. The coarse material will fall near the fan, the fine portion 

 farther away. Very fine dust is blown out into the air and does not fall on the 

 paper. 



A technique often employed in micropaleontological work, and having 

 definite advantages in some lithologic work, is that of examining the samples 

 while completely immersed in water. This method is good when the samples are 

 dusty, as described in the preceding paragraph. 



A black plastic dish 14 inch deep and 3 to 4 inches in diameter is sub- 

 stituted for the scoop tray. The sample is spread evenly over the bottom, and 

 enough water is added to cover the chips completely. 



The advantages of this procedure are (1) the effects of dusty or pulverized 

 materials on the chip are eliminated, (2) fine details of the rock are sharply 

 defined, and (3) colors are more vivid. The disadvantages are (1) it is slow 

 and dirty work, (2) the samples must be dried before replacement in the envel- 

 opes, (3) the tones of gray shales are deepened until subtle differences are 

 difficult to distinguish, and (4) acid reactions are unreliable with wet chips. 



The immersion technique is applicable to field use where samples obtained 

 from the drilling well must be examined immediately while still wet. Wet samples 

 that are not immersed in water are difficult to analyze. 



22 



