shops or five-and-ten stores as clear model-airplane dope; and (3) lacquer or 

 clear dope thinner, which is used to clean the brush. 



The log should be laid flat on a table and the lacquer applied to the color 

 column in a thin, even coat. After allowing a few minutes for drying, one 

 should apply the second coat, which fixes the colors and renders them water- 

 proof. 



A plastic spray called Krylon, in an inexpensive pressured container, is also 

 satisfactory. The entire log may be sprayed two or three coats and made 

 waterproof. If only the color column is to be treated, the remainder of the 

 strip must be masked from the spray. 



One should not use varnish, which turns amber with age, or white shellac, 

 in which the alcohol solvent will also affect the pencil colors. 



Logs sometimes must be shortened in order to fit into file cabinets, but 

 folding ruins the log. The log should be cut straight across and then rejoined 

 with Dennison's gummed cloth library tape, li/2 to 2 inches wide. This tape 

 serves as a hinge, and, if firmly burnished down, will last almost indefinitely. The 

 top edge of the strip may be bound with tape and punched for hanging on pegs. 



Percentage Strip Logs 



In some parts of the country, percentage logs are more widely used than 

 the interpretive logs described in the preceding pages. Two practices are fol- 

 lowed in the construction of percentage logs: 



(1) The unqualified percentage log shows the percentage of each lithology 

 in the entire sample, without prior separation of the material thought to be 

 caved from up the hole. 



(2) The qualified percentage log shows the percentages of lithologies 

 interpreted as freshly cut in the sample interval. The interpreted cavings do 

 not enter into the calculations of percentage. This is the type of log most com- 

 monly used, and it is certainly the better of the two. 



The lithologies are plotted in the color symbols used for interpretive logs. 

 The strip is ruled vertically in intervals of 5 or 10 percent, and the percentages 

 of the lithologies are plotted accordingly (fig. 3-7). 



Although percentage logs are sometimes preferred, they have certain dis- 

 advantages. The relationships of stratigraphic units within a sample interval 

 are shown horizontally, although they actually occur in vertical sequence. 

 Stratigraphic interpretation of the samples is therefore passed on to the user 

 of the log, who may never have seen the rocks. The sample examination is 

 reduced largely to a mechanical process, which does not permit the sample man 

 to reconstruct the stratigraphic column as it actually occurs. 



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