98 THE UNITED STATES GEOLOGICAL SURVEY. [bull.22 
Publications of the United States Geological Surra/, by years- — Continued. 
Printed pages. 
Plates and 
maps. 
1901— Continued. 
6 geologic folios (70, 71, 72, 73, 74, 75) 
'.'special reports on Alaska (Reconnaissances in the Cape Nome and 
Norton Bay regions in 1900; and Report on the Copper River dis- 
trict) 
316 
1902. 
2 annual reports (22d, part of, and 23d) 
1 monograph (XLI) 
9 professional papers (1, 2, 3, 4, 5, 6, 7, 8, 10) 
18 bulletins (179, 188, 189, 190, 191, 192, 193, 194, 195, 196, 197, 198, 199, 
200, 201, 202, 203, 204, 207) 
18 water-supply and irrigation papers (57,58,59,60,61,62,63,64,65, 
66, 67, 68, 69, 70, 71, 72, 73, 74) 
1 report on mineral resources (for 1901) , 
10 geologic folios (76, 77, 78, 79, 80, 81, 82, 83, 84, 85) 
1903. 
1,670 
802 
845 
3, 959 
1,965 
996 
119 
302 
317 
1 annual report (24th) 
1 reclamation annual (1st) 
4monographs (XLII, XLIII, XLIV, XLV) I 1,341 
10 professional papers (9, 11, 12, 13, 14, 15, 16, 17, 18, 19) 2, 255 
16 bulletins (205, 206, 208, 209, 210, 211, 212, 213, 214, 215, 216, 217, 218, 
219, 220, 221) 2, 693 
14 water-supply and irrigation papers (75,76,77,78,79,80,81,82,83, I 
84, 85, 86, 87, 88) .' ' 2, 562 
1 report on mineral resources (for 1902) about J 1, 000 
15 geologic folios (86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100) .... 128 
HI 
26 
85 
188 
67 
10,356 
Grand total 
26 
47 
US 
171 
10,598 
119, 353 
603 
641 
727 
Section of Geologic Maps. 
The classification and geologic nomenclature adopted by the United 
States Geological Survey on its organization was based on the works 
of such eminent geologists as Dana and Le Conte, and has been the 
foundation of all later systems of the Survey. A scheme of colors for, 
use on maps was provisionally adopted in 1881. It consisted of a 
limited number of colors, each representing a definite period of geo- \ 
logic time, and of a few patterns, which were used indiscriminately 
for all classes of rock. 
The printing of geologic maps in colors was at that time an experi- 
ment, and the plan adopted by the Survey was tentative. It was soon 
found inadequate, and but few geologic maps were printed before 
1889. Such as were published prior to that date have since been 
reissued upon a more comprehensive plan which was adopted in that 
year as a result of a conference of geologists. 
This conference adopted rules of geologic nomenclature and a sys-l 
tern of classification which accorded with the progress made in the 
