298 BIBLIOGRAPHY AND CARTOGRAPHY

WEEKS, T. D. Manganese.

Mineral Resources U. S., 1885, Washington, 1886, p. 344.

Refers to deposits of black oxide of manganese " at Brookville, Montgomery county,
and another on the Maryland side of the Potomac across from Harper's Ferry. None
at present mined in the state."

WILLIAMS, G. H. The Gabbros and Associated Hornblende Rocks
occurring in the neighborhood of Baltimore, Md.

Bull. U. S. Geol. Surv. No. 28, 1886, 78 pp., 4 pls.

House Misc. Doc., 49th Cong., 2nd sess., vol. viii, No. 163.

A petrographic study of these rocks accompanied by many photomicrographs,
analyses and a map showing the position of actual outcrops and the distribution of
rocks Inferred therefrom.

———— On a remarkable crystal of pyrite from Baltimore County,
Maryland.

Johns Hopkins Univ. Cir. No. 53, vol. vi, 1886, p. 30.

Found west of Cromwell's Bridge road, opposite Summerfield Station. Peculiar
luster, color and merohedrism suggest columblte.

1887.

ASHBURNER, CHAS. A. Coal.

Mineral Resources U. S., 1886, Washington, 1887, pp. 224-279.
Statistics, notes, and companies of George's Creek coal district and also the ship-
ments from 1S42-1886.

BIRKINBINE, J. The Iron Ores East of the Mississippi river.

Idem, p. 77.

Analysis of brown hematite from central Maryland.

DAY, D. T. Infusorial Earth.
Idem, p. 587.

States that " the production for the year amounted to 1200 short tons with a spot
value of $6000." The source is " near Dunkirk, Calvert county."

DUNCAN, P. MARTIN. On a new Genus of the Madreporaria (Gly-
phastrea Forbesi, Ed. and H. from the Tertiaries of Md., U. S., with
Plates).

Quart. Jour. Geol. Soc., London, vol. xliii, 1887, pp. 24-32.

Refers to writings by Milne-Edwards, Julius Halme, M. de Fromentel and others
and gives a full description of Glyphastrea Forbesl.

HITCHCOCK, C. H. The Geological Map of the United States.

Proc. Amer. Inst. Min. Eng., vol. xv, 1887, pp. 465-488.

Gives an historical account of the geological maps previously published and shows
one drawn in the colors adopted by the International Geological Congress.

McGEE, W J The Columbia Formation.

Proc. Amer. Assoc. Adv. Sci., vol. xxxvi, 1887, pp. 221-222.
Summary of information concerning the formation.