40 Dr. J. W. Hvans—Geological Maps. 
considerations lead some to foretell a coming world shortage which 
will be little less than a famine. 
On the other hand, great reserves of unworked copper-ore 
undoubtedly exist in different parts of the world, and in course of 
time an increased production may be looked for from the resources 
of Mexico, Chile, and Peru in Central and Southern America, from 
the Altai, the Kirghiz Steppes, and the Urals in Russia, from the 
Belgian Congo in Central Africa, and from South-West Africa. 
Whether future supplies will equal the demands there are not 
sufficient data at hand to determine. 
The Representation of Stratigraphical Divisions 
by Shading. 
By Dr. J. W. Evans, F.R.S. 
ae and white shading is frequently employed in geological 
maps and sketches, but there is a remarkable absence of 
uniformity in the means by which different strata have been 
represented. 
There are three purposes for which shading may be employed in 
geclogical maps, but these cannot as a rule be satisfactorily effected 
on the same map. It may be desired to express (1) the lithclogical 
characters of the rocks, (2) their stratigraphical position, and (3) 
their structural relations. For the first purpose it is convenient to 
use the same conventional shading as is employed in diagrams of 
sections. It is mainly with the second that I shall deal in the 
present article. For the third purpose little has yet been done, and 
I hope to consider the subject on another occasion. 
I devised the system of denoting the different divisions of the 
geological succession, which I shall now describe, for the small scale 
geological maps published in the portion of the Handbuch der regionalen 
Geologie dealing with the British Isles. One of these is reproduced, 
on a reduced scale in this issue of the GrotogicaL Macazine. The 
geological boundaries were drawn by Dr. Morley Davies and the 
shading by Miss Reeks, Technical Artist to the Imperial College of 
Science and Technology. 
In this system the pre-Cambrian rocks are distinguished by a 
north-east and south-west direction of shading (the Charnian 
strike), the older Paleozoic—Cambrian, Ordovician, and Silurian— 
by a north-east and south-west direction, the later Paleeozoic— 
Devonian, Carboniferous, and Permian—by a north and south 
direction, ‘that of the Pennine range, and the Mesozoic by an east and 
west direction (Hercynian). 
The Kainozoic is indicated by crosses and the Quaternary or 
Anthropozoic by small circles or “ birds” (~~). In the subdivisions. 
of the strata expressed by each direction of shading, the older 
rocks are distinguished by continuous lines and the later by 
1 Sidney Brooks in the North American Review. 
