2 
In geological map printing, the object in view, exclusive of the topo- 
graphical base, is to produce the legibility, distinctness, and contrast 
requisite for clear illustration of the geological formations and features. 
Different parts of a map require to be represented by deep and light 
colours so disposed that the above conditions are satisfied, and yet a 
pleasing general effect also produced. It follows that the colours should 
not, as in photographic halftone printing, blend in an infinite gradation of 
tones, but that a limited number of well-defined colours and tints of uniform 
range of depths should be selected. 
The desired result is obtained in this process by the use of flat colours 
(pigments with admixture of white to a determined depth of colour), 
in combination with line-tints of same colours from finely ruled transfer 
plates. When flat colours and line-tints are laid on three printing stones, 
with plate rulings in appropriate positions, and are printed over one another 
in yellow, blue, and carmine inks, all the colours will be produced with 
the required contrast and distinctiveness. 
By the use of ruled, patterned, or stippled plates of various weights, 
a great number of colour distinctions or effects may be produced; in 
practice, with few exceptions, a flat tint and one or two line-tints from 
parallel-ruled or cross-ruled plates in each colour are sufficient. For 
the maps of the Geological Survey, Canada, satisfactory results are uni- 
formly obtained by using each primary colour in full tint and in one line 
tint from a ruled plate the lines on which are inch thick, and inch 
apart. . Such a ruling when printed in colour has a colour intensity equal 
to about one-third of that of a solid printing of the same pigment. 
_______ 
— 
JTUvt 
tint 
— -Lube - — 
— hut. 
- 
JtUxJt 
tint 
Linr 
tint 
Bine 
Carmine. 
Figure. 1 . Direction of parallel rulings on printing stones. 
The selection of ruled plates as well as the density of the colours should 
be carefully considered in view of the purpose of the intended maps. 
Coarse patterns or rulings are in some cases required for special features, 
and cross-ruling is often used. 
Parallel rulings for yellow printing are always transferred to stone 
horizontally, for blue vertically, and for carmine diagonally (Figure 1). 
If more than two distinctions in each fundamental colour are required, a 
parallel-ruled plate with heavier and closer ruling is in some cases used 
in addition and in preference to one cross-ruled plate. 
With cross-ruled plates, care must be taken in transferring to stone 
that the rulings for the different colours are laid on their respective stones 
in such positions that they will fall on each other at angles sufficiently 
large to avoid the production of motley colour surfaces. The rulings of 
cross-ruled plates, like the photographic halftone screens, are made at right 
