3 
angles; if two colours with such plates are to be printed in combination, 
one plate may be transferred to stone with lines laid horizontally and verti- 
cally, and the other, diagonally at an angle of 45 degrees (Figure 2 A). If 
the three colours are to be combined — which is seldom required — the 
second and third transfers must be made so that their rulings are at angles 
of respectively 30 and 60 degrees with those of the first transfer (Figure 2 B). 
\ 
^ \ 
! > „ \ 
bet - 0 
i i -\ 
/, 'Ist.trerrLsfer 
s'; 
/ / 
/ 
t 
/ 
/ 
\ 
\ 
\ 
JS. ThJ'&e. I*ruiJ±ruj& 
Figure 2. Relative positions of colour cross-rulings on printing stones. 
Line-tint plates may be engraved especially for this process, but 
suitable plates of all descriptions are available in the lithographic trade. 
The process entails no difficult lithographic manipulation, and printing 
stones are prepared in the ordinary way by a skilled lithographic map 
artist who has only to follow definite specifications accompanied by copy 
showing the colour results, or if necessary, copy showing the required 
make-up of each colour stone (See Plates I, II, III, IV). 
In planning colour schemes and specifications by this process for 
geological maps, the following conditions may be kept in mind: 
(1) The selection of appropriate single or combined colours and tints 
for each map or set of map-sheets. Set schemes of map colouring for the 
whole range of geological formations, or reservation of certain colours or 
tints for particular geological formations on all maps, have been found to 
be objectionable to a degree incommensurate with the advantages of 
uniformity. 
(2) Parallel line-tints of different colours, or combined line-tints 
of two or three colours, are preferable for large areas. Flat tints or com- 
binations of flat tints are better for small areas. 
(3) Flat tints of primary colours only, or extra printings in opaque 
colours, are best for very small features and those of special character 
such as dykes, symbols, etc., where the extreme precision of registration 
would preclude combination of flat tints. 
(4) Harmony and contrast of colours should be sought, as well as 
selection of proper neighbouring colours and tints to avoid or counteract 
the distorting optical effect of one colour upon an adjacent one. 
Transparent pigments as permanent as possible should be used. 
Such pigments should have no chemical reaction when mixed and should 
be as resistant as possible to the bleaching effect of strong light. They 
