156 Subsurface Geologic Methods 



of the original sample. In all samples the data for percentage-percentage 

 plotting must be calculated or a table employed. A major disadvantage 

 of the method is that a constituent which is ten percent of a residue, 

 which in turn is ten percent of the original sample, requires the plotting 

 of a 0.01-percent space on the log. Such a small space is difficult to 

 plot as well as to identify in later study and correlation work. Though 

 a ten-percent residue is ample for determination, many residues are less 

 than five percent. Small but significant and diagnostic constituents would 

 be obscure and very difficult to differentiate on a log. This method of 

 plotting has an advantage in showing the percentage relations of the 

 constituents at a glance, eliminating the examination of both the per- 

 centage and constituent columns of the first method discussed. 



The third method of assembling data is a tabulation. A number of 

 columns, headed by the names of significant types of residues, allow space 

 for tabulating the percentage of each constituent and for symbols with 

 superscripts or abbreviations added as modifying descriptions. This 

 method is not suitable for correlation work and cannot be used in con- 

 junction with the standard scale of plotted logs. It is useful only for 

 tabulating data for the use of log plotters or others making strip logs or 

 for consultation when detailed information not amenable to log plotting 

 is needed. 



The first method has been found to be the most satisfactory, and it is 

 recommended, although several versions of the three have been used, and 

 other combinations may be devised. It is most desirable for all workers 

 to use a standard set of symbols, superscripts, and overprints. This applies 

 especially to new workers entering the field of insoluble residues. Work- 

 ers could then examine, discuss, interpret, and publish insoluble-residue 

 correlations and identifications with a common background. Many workers 

 will find it difficult or unwise to change systems of graphic description, 

 because consistence with former usage is necessary where logs or records 

 are involved. 



The sets of symbols and overprints given here are recommended for 

 standardized use. They are essentially those used by the Missouri Geolog- 

 ical Survey. Certain modifications, combinations, and additions make the 

 symbols conform to the recently standardized terminology. Color was 

 used formerly by the writer to indicate the observed color of the chert; 

 but color is now used to indicate the type of chert, and chert colors are 

 indicated in a separate column. 



Hendricks ^"^ uses a set of letters, lines, bars, or graphics without 

 color. If the percentage of the residues, the color of the residues, or the 

 percentage of the constituents is not desired or necessary, the set of sym- 

 bols is adaptable. Many of them may be made with a standard typewriter. 



^"'^ Hendricks, Leo, Subsurface Divisions of the Ellenburger in North-Central Texas: Texas Univ. 

 Bur. Econ. Geology Bull. 3945, pp. 923-968, 1940. 



