weeks] PALEONTOLOGY, PETROLOGY, AND MINERALOGY, 189G. 71 
530 Peale (A. C). Three Forks folio, Montana. 
U. S. Geol. Surv., Gcol. Atlas of U. S., folio No. 24, 1896. 
Describes the physiography and geologic history of the region, the 
character and distribution of Archean, Algonkian, Cambrian, Devo- 
nian, Carboniferous, Juratrias, Cretaceous, Tertiary, Pleistocene, and 
igneous rocks. Includes a discussion of the geologic structure, the 
economic features, and topographic, geologic, economic, and structure 
section maps, and a sheet of columnar sections. 
531 Pearce (Richard). The mode of occurrence of gold in the ores of 
the Cripple Creek district [Colorado]. 
Read before the Colorado Scientific Society, in Denver, Colo., Jan. 8, 
1894, 8 pp. 
Describes the characters of the ores and discusses briefly their origin. 
532 Further notes on Cripple Creek ores [Colorado]. 
Read before the Colorado Scientific Society, in Denver, Colo., April 5. 
1894, 7 pp., 1 pi. 
Gives additional results of the author's study of these ores. 
533 Some notes on the occurrence of uraninite in Colorado. 
Read before the Colorado Scientific Society, in Denver, Colo., Sept. 
9, 1895, 3 pp. 
534 ]S"otes on the occurrence of a rich silver and gold mineral con- 
taining tellurium, in the Griffith lode, near Georgetown, 
Clear Creek County, Colo. 
Read before the Colorado Scientific Society, in Denver, Colo., Oct. 5, 
1896, 2 pp. 
Describes the characters of the mineral and gives its chemical com- 
position. 
535 Notes on the occurrence of tellurium in an oxidized form in 
Montana. 
Read before the Colorado Scientific Society, in Denver, Colo., Nov. 2, 
1896, 2 pp. 
Describes the chemical characters of the material. 
53(3 Pechin ( Edmund C). The Oriskany ores at Rich Patch mines, Va. 
Eng. and Mg. Jour., vol. lxi, pp. 113, 134 and 159-160, 1896. 
Describes the geologic occurrence of the brown hematite ores and the 
extent of the mining developments. 
537 Peckham (S. P.). What is bitumen ! 
Sci. Amer. Snppl., vol. xli, pp. 17071-17072, and 17083-17084, 1896. 
Describes the character of bitumen and allied substances and their 
occurrence in various parts of the world. 
538 Penfield (S. L.). On pearceite, a sulpharsenite of silver, and on 
the crystallization of polybasite. 
Am. Jour. Sci., 4th ser., vol. ii, pp. 17-29, 1896. 
Discusses the relations of the sulphantimonites and sulpharsenites of 
silver. Proposes the name pearceite for the sulpharsenite species, and 
describes the chemical composition and crystallization of material from 
the Drumlummon mine, Montana. Describes the crystallization of poly- 
basite from Colorado, and discusses the relations of pearceite and poly- 
basite to each other and to other minerals. 
