494 JOURNAL OF THS WASHINGTON ACADEMY OF SCIENCES VOL. 11, NO. 20 



ABSTRACTS 



Authors of scientific papers are requested to see that abstracts, preferably prepared 

 and signed by themselves, are fonvarded promptly to the editors. The abstracts should 

 conform in length and general style to those appearing in this issue. 



GEOI^OGY. — Contact-metam Orphic tungsten deposits of the United States. 

 Frank L. Hess and Esper S. Larsen. U. S. Geol. Surv. Bull. 725-D. 

 Pp. 65(245-309). 1921. 



Contact-metamorphic tungsten deposits have been formed through the 

 combined action of the heat and solutions emanating from a cooling intrusive 

 granitic magma on limestones and the other intruded rocks and to a less 

 extent on the invading granitic rock itself, by which the rocks are altered to 

 or replaced by an aggregate of garnet, epidote, diopside, quartz, calcite, 

 scheelite, and other minerals. Most deposits of this class are at or very near 

 the contacts, and they clearh^ represent replacement of the limestones and 

 other rocks. The tungsten mineral of such deposits is invariably scheelite. 



Most of the known contact-metamorphic tungsten deposits in the United 

 vStates are in the Great Basin region in California and Nevada and north- 

 western Utah, but Oregon, Arizona, and New Mexico are known to contain 

 one deposit each, arid it is probable that other such deposits will be found in 

 widely different parts of the country. 



The geologic features of contact-metamorphic deposits and the causes of 

 metamorphism are discussed. Most of the paper is made up of a brief pre- 

 liminary description of the contact-metamorphic scheelite deposits in the 

 western United States. R. W. StonE- 



GEOLOGY.- — Chrome ores in Pennsylvania, Maryland and North Carolina. 

 Eleanora Bliss Knopf and J. Volney Lewis. U.S. Geol. vSurv. Bull. 

 725-B. Pp. 55 (85-139). 1921. 



Chrome ore was discovered in Maryland as early as 1827. Until 1860 

 Maryland and Pennsylvania furnished the world's supply of chrome ore, 

 but in 1860 the chief source of the world's supply was transferred to Turkey. 

 Since 1882 practically all of the output of chrome ore in the United States 

 has come from the Pacific coast, and the industry in the Eastern States has 

 lain dormant. 



The chromite is found in rock ore and in alluvial sand. The rock ore is 

 both massive and granular. It occurs in serpentinized pyroxenites and 

 peridotites that probably represent ultrafemic differentiates of a gabbro in- 

 trusion. The massive ore occurs in pockets of variable size. The ore occurs 

 at intervals in a belt 50 miles long that extends from the southwest corner 

 of Chester County, Pa., to the neighborhood of Baltimore, Md. It has 

 probably originated by the sinking of chromite grains during the crystalli- 

 zation of a highly magnesian magma. 



The chrome ores of North Carolina occur in granular olivine rocks (peri- 

 dotites), which form numerous small isolated outcrops in a belt 5 to 25 miles 

 wide throughout the mountainous western part of the State, a distance of 

 200 miles. 



