296 The American Geologist. November, 1905 
J\ T o. C. — Estudio de la hidrologia subterranea de la region de Caderey- 
ta Mendez, E. de Queretaro; por el Ing. J. D. Villarello. — 1904. 
— 58 pp., 2 lam. 
.No. 7. — Estudio de una muestra de grafita de Ejutla, Estado de Oaxa- 
ca, por el Ing. J. D. Villarello. — Analisis de las cenizas del vol- 
can de Santa Maria, Guatemala, yor el Ing. E. Ordonez. — 
1904.— 26 pp. 
No. 8. — Hidrologia subterranea de los alrededores de Queretaro, 
por el Ing. J. D. Villarello. — 1905. — 56 pp., 3 laminae y 2 
figuras. 
-City of Mexico, Aug. 25, 1905. 
SERPENTINES IN THE NEIGHBORHOOD OF PHILADELPHIA. 
Anna I. Jonas, Bryn Mawr, Pa. 
The object of this paper is to give a brief review of the 
■occurrence and origin of the known serpentines, and to 
describe in particular, the serpentine dykes in the neigh- 
borhood of Philadelphia, Penna. 
It is generally conceded that serpentine, wherever oc- 
curring as a mineral or a rock, is a secondary product 
formed in the zone of katamorphism and that it is devel- 
oped by the alteration of non-aluminous, ferro-magnesian 
silicates ; olivine, the pyroxenes, anthophyllite, tremolite and 
actinolite. In a less number of cases serpentine has been 
derived from a limestone. 
An entire rock mass may be composed exclusively of 
serpentine, or the rock may contain remains of the original 
minerals from which the serpentine was derived. The 
phvsical characters of the rock serpentine are therefore 
somewhat modified by the presence of associated minerals. 
In color serpentine has a wide range through all shades of 
green, brown and reddish brown. Its texture depends 
largely on the mineral from which it was derived; serpen- 
tine formed by the hydration of olivine is massive; that 
variety formed by the alteration of an amphibole is usually 
fibrous. That variety which results from the alteration of 
prvoxene may be described as massive. 
Since serpentine, a katamorphic product, is not easily 
weathered, it usually forms a ridge scantily covered with 
a sterile soil composed of silica, magnesia and stained with 
iron oxide. 
