450 PROCEEDINGS OF THE ACADEMY OF [Part III 



Chromite Deposits. 



The chromite deposits occur exclusively in the meta-pyroxenite 

 and meta-periodotite area. The principal mines, now all abandoned, 

 are hsted below, with their reputed production.^ 



Line Pit, three-quarters of a mile northwest of Rock Springs 

 cross-roads, Maryland; 1,000 tons. This chromite body presents 

 a number of unusual features, and is in some respects the most 

 remarkable deposit in the district. 



The deposit may be described as a rough, irregular cylindrical 

 mass, with the average diameters of 5 by 8 feet, which has been 

 worked to a depth of about 250 feet. The chromite body pitches 

 S 75° E at an angle of about 60°. 



This rough cylindrical mass is surrounded by a thick sheathing 

 of a translucent green, jade-like serpentine known as williamsite, 

 averaging about a foot in thickness, beyond which lie the ordinary 

 types of serpentine. Thick tabular masses of williamsite form 

 partings in the chromite deposit, while veins of it may extend 

 into the serpentine walls. Fractures in the chromite are filled 

 with clinochlore or kammererite. Many veins of magnesite, 

 containing residual masses of green serpentine, were found cutting 

 the chromite deposit and the serpentine in the lower levels. 



Reynolds' Mine, one and a half miles south of Wrightsdale; pro- 

 duction small. 



Wood's Mine, one mile southwest of Lee's Mill; 120,000 tons. 

 The Wood's Mine chromite deposit formed an enormous, irregular 

 mass, in a dark green serpentine, which assumes a brown coating on 

 weathering. The deposit was worked to a depth of 720 feet. The 

 greatest length along the strike was 300 feet, with a width of 10 

 to 35 feet, and a pitch of 40° to 60°. The strike was nearly E. and 

 W. at the outcrop, and N. and S. on the lower levels. Branches of 

 the chromite body occasionally extended into the serpentine. " 



Adjacent to the chromite, the serpentine showed a prismatic 

 structure, the cracks of which extended normally to the chromite 

 for a distance of a half inch or more, and were filled with deweylite 

 or magnesite. This secondary phenomenon occurred during the 

 serpentinization of the peridotite or pyroxenite, and indicates that 



^ For a map see these Proceedings Vol. 73, p. 174. 

 ^Persifor Frazer, Jr., Second Geol. Surv. Penna. Rep. C3, 1880, 192-196. 

 WilHam Glenn, Trans. Am. Inst. Min. Eng. 25, 481-499, 1896. 



