414 J. F. KEMP — GEOLOGICAL BOOK-KEEPING 



The use of ninths also keeps us within the limits of single digits. For 

 greater accuracy each ninth may now be considered to be divided into 

 other ninths, as shown in 12, 1.6, and beyond this it is almost never 

 necessary to go. The star (*) on the map, figure 1, is in 2,369 (read, 

 two, three, six, nine). The plus sign (+) is in 11,327 ; the multiplica- 

 tion sign (X) in 22,455. In the note book one would merely record 

 11,327 and the observation, after placing a dot or little cross on the map- 



For field use the maps, after being drawn with squares, should be 

 trimmed of the borders to the quadrangular lines and cut in thirds along 

 the parallels of latitude. Each strip is then doubled back on itself once, 

 map side out, and folded forward in quarters, map side in, so as to make 

 a little accordion-like book, which can be tied in the note book and 

 turned over like the leaves of a book. On the back of each should be 

 written the name of the quadrangle, and " north third," " middle third," 

 and " south third," as the case may be, and the year or years in which 

 the maps were used in the field. 



When ruled in squares of this size there will always remain except in 

 a few fortunate latitudes a strip at the right side of the map which does 

 not make an even inch. Latitudes 41 degrees 30 minutes to 42 degrees, 

 for example, are almost exactly divisible, but those to. the north and 

 the south are not. There will also always remain at the bottom of the 

 map an incomplete lower row about half a square high, and in the 

 eighties. These fractions, however, cause no difficulty, because the 

 proper numbers of the parts remaining are perfectly apparent and the 

 others simply drop out. 



In cutting up the maps into three strips along the parallels of latitude 

 other squares are cut into fractional parts, but this also occasions no 

 serious trouble, because the order of enumeration being invariable, if we 

 have the numbers of one row before us, those of all the others adjacent 

 are at once apparent. Thus in figure 1, in the fractional strip on the 

 right, we can locate ourselves just as well from the column of the squares, 

 2, 12, and 22, as if we actually had the appropriate numbers, 3, 13, and 

 23, which are cut off. 



As a variation and perhaps as an improvement upon the above method 

 of drawing the squares, it is, of course, possible to place the double lines 

 at intervals of three squares, so that each square of double lines encloses 

 nine of single lines, then number in the same way and go down to any 

 desired accuracy by subdivisions of ninths. Or it is possible, as the sheets 

 are all divided into nine parts by the intersections of the meridians and 

 parallels, to make the rectangles, thus afforded, the basis of the primary 

 numbering and then go down by ninths, never needing double figures for 

 the large unit area, but this latter plan throws us out of the mile-on-a-side 

 squares which are very useful scales of distance. 



