256 The American GeoJoyl.sf. octo))er, i89i 
place of origin, but that they originated at different places upon the 
earth. We have parallelism in separate places, but the parallelism is 
defective in the Laramie. 
Mr. G. K. Gilltert was of the opinion that many methods of correlat'on 
must be used. He doubted the trustworthiness of the correlation of non- 
fossiliferous rocks by comparative change, even locally. He thought the 
abundance and scarcity of fossil forms comparable with lithologic differ- 
ences, and considered the simple occurrence of a species as valuable for 
purposes of correlation as its abundance. 
Prof. Van Hise explained that the distinction between the Algonkian 
and the Archa-an has not been widely made in Europe, l)ecau8e there, as 
in the Appalachian region, later and powerful dynamic movements have 
repeatedly occurred. 
Prof. E. D. Cope added that life in its progress on the earth differed from 
minerals and rocks in that it has its own laws, which give it an indepen- 
dent element. 
Announcements were made by Secretary Emmons, and the meeting 
adjourned at 1 o'clock until 11 o'clock a. m. Monday, August 31st. 
SESSION OF Aco. 31, 1891, 11:2.1 a. >r. 
Prof. James Hall, Vice-President, in the chair. 
Announcements were made bj' Mr. S. F. Emmons, General Secretarj*. 
Subject for discussion: Map-coloring and Cartographj'. 
Major J. W. Powell exhibited charts illustrating the color system used 
by the U. S. Geological Survey, explained the methods of using the colors, 
and gave the reasons for them. The colors"assigned to rocks of different 
ages are as follows: 
Period. Period color. Mark. 
1. Neocene Orange N. 
2. Eocene Yellow E. 
'i. Cretaceous Yellow-green . . K. 
4. Jura Trias Blue-green 
5. Carboniferous Blue C. 
6. Devonian Violet D. 
7. Silurian Purple S. 
8. Cambrian Pink 
6. Algonkian Red A. 
The colors are used to designate geologic periods, patterns of these 
colors designate formations ; -minor divisions are usually relegated to the 
text. The number of patterns for designating formations can be 
indefinitely enlarged, but follow a definite system. 
.Mr. Joseph Wilcox showed that in the scheme described by major 
Powell the colors were not evenly distributed tlirough the chromatic 
scale. 
Prof. C. R. Van Hise pointed out that Arch.ian rocks are shown l)y a 
brown underprint, and that niftamorphic rocks of known age are given 
the color of the corresponding unaltered rocks. 
Major Powell explained that it was not attempted to select colors 
