1921] NATURAL SCIENCES OF PHILADELPHIA. 451 



the chroiiiite deposit was formed prior to the serpentinization. A 

 similar structure is found in the serpentine adjacent to magnetite 

 veins in Brinton's Quarry, three miles south of West Chester, Chester 

 County, Penna. 



The following minerals were found associated with the chromite, 

 clinochlore, kammererite, uvarovite, brucite, hydromagnesite, 

 genthite, and zaratite. 



i^ecZPtY, one-half mile northeast of Line Pit; production unknown. 



Jenkin's Pit, three-eighths of a mile northeast of Red Pit; 1,000 

 tons. This mine has been abandoned for a number of years, and the 

 writer's observations were limited to the material on the dumps. 



In addition to massive chromite much disseminated chrome, 

 known as "birds -eye ore" was mined. The chromite deposits occurred 

 in dark brown, light to dark-greenish, or almost black serpentines, 

 which under the hand lens are seen to consist of greenish translucent 

 grains. Under the microscope the serpentine shows characteristic 

 mesh structure with residual grains of olivine (fig. 1). The dissem- 

 inated chromite occurs as rounded grains in a light greenish ser- 

 pentine, ■ with residual olivine. Occasional grains of serpentinized 

 olivine are found entirely enclosed by chromite (fig. 2), and studj^ 

 of thin sections indicates that the chromite crystallized out from 

 the magma contemporaneously with the olivine. 



The clinochlore and kammererite form druses in the chromite, 

 having been deposited by hydrothermal solutions, perhaps during 

 the process of serpentinization. The genthite and zaratite are due 

 to the weathering of minute amounts of an undetermined nickel sul- 

 fide present in the chromite. 



Carter's Mwe, three-eighths of a mile east of Wood's Mine; 400 tons. 



Scott's Mine, two miles southwest of Nottingham; 3,000 tons. 



Moro Phillips' Mine, one mile south of Nottingham; 250 tons. 



In addition a number of smaller pits have produced from 20 to 

 50 tons, while more than 5,000 tons of sand chrome has been reported 

 to have been obtained by washing the stream sands of the region. 



An abandoned magnetite mine is situated one-and-a-quarter miles 

 northeast Rock Springs cross-roads, Maryland. 



The Serpentines. The serpentines forming the country rock are 

 largely brownish or greenish rocks, which are seen under the hand 

 lens to consist of small greenish, translucent grains, separated by 

 films of magnetite particles. Under the microscope some of the 



