Basic Rocks of Northeastern Maryland. — Leonard. 157 
Two varieties of pyroxenyte occur in northeastern Mary- 
land, namely, a hypersthene-diallage rock ( websteryte) and a 
pure hypersthene rock (hypersthenyte.) The latter, which has 
a coarsely g-ranular texture, is the more abundant, being found 
at a number of different points, but especially in the vicinty of 
Oakwood and a short distance south of Conowingo. At the 
fomier locality the hypersthenyte seems to occur as a facies of 
the noryte, along the border between the latter and the ser- 
pentine, while at the last named locality the rock forms a dike 
•or dikes in the noryte. In places the hypersthenyte contains 
some olivine and thus passes into peridotyte. The websteryte 
is found near Oakwood and at various points, but perhaps the 
best locality for this rock is one and a half miles west of Sylmar. 
At this same place there is an outcrop of pei^idotyte along the 
road near the crossing of the west branch of Stone run. Like 
the other pyroxenyte type the websteryte is frequently found 
near the edge of the noryte mass, closely associated with the 
serpentine. The rock is a very coarse-grained aggregate, the 
allotriomorphic individuals often measuring one-quarter of 
an inch (6 to 7 millimeters) in diameter. Both varieties of 
pyroxenyte are remarkable for their freshness, many of them 
having undergone no alteration whatever. 
Pure pyroxene rocks, which are quite abundant in Mary- 
land, were first described from here by G. H. Williams* who 
recognized two well marked types as occurring within the state, 
namely, a hypersthene (or bronzite )-diallage rock and one 
composed of the same orthorhombic pyroxene and diopside. 
To these two types a third must now be added, namely, one 
composed almost wholly of hypersthene — the hypersthenyte. 
The first type above mentioned occurs in Baltimore, Har- 
ford and Cecil counties, Maryland, and in Chester county, 
Pennsylvania. The latter occurrence is described by F. D. 
Chester, who states that the rock consists mainly of bronzite 
and diallage which are usually nnicli altered. f The second 
type, the bronzite-diopside aggregate, occurs near Hebbville P. 
O., Baltimore county, and rcseml)les the pyroxenyte from near 
Webster, North Carolina, assumed as the type locality b\- Will- 
iams. 
*Amer. Geol., July, 1890, nn. 35-49. 
fAnn. Kept. Geol. Siu-y., Tenn., for 1887. p. O."). 1SS0. 
