PENNSYLVANIA. ST) 
age and the relative facility with which they are quarried make it possible to supply 
them at low figures. On the other hand they are remarkably well adapted by their 
softness and the thickness of the beds for mill-stock purposes and particularly for 
blackboards and other indoor objects. 
All the more important features of the slates of Pennsylvania will be found in tabu- 
lar form in the section on the comparative characteristics of slates ( p. 124). 
PENNSYLVANIA AND MARYLAND (PEACH BOTTOM) SLATE. 
This slate deposit seems to have derived its name from that of a small village one- 
fourth mile west of the Susquehanna River, formerly a sort of a port in the now 
disused canal which follows the river. This village is in a triangular township of 
the same name, which is bounded by the Maryland line on the south, the river on 
the northeast, and in part by Muddy Creek on the northwest, and which forms the 
southeast corner of York County, Pa. 
Geological relations. — The only available geological maps of the region are those 
of the two Pennsylvania geological surveys and of the Maryland geological survey. « 
The slate forms a belt and low ridge from one-fifth to one-half mile wide, which 
extends from a point about a mile northeast of the Susquehanna, in the town of 
Fulton, in Lancaster County, Pa., in a southwest direction across the river and across 
Peach Bottom township in York County, and continues for about 3 miles in the same 
direction into the town of Cardiff, in Harford County, Md. Its total length is about 
10 miles, of which 1 mile lies in Lancaster County, Pa,, 1.] mile:3 are submerged by 
the Susquehanna, i\ are in York County, Pa., and about 8 miles are in Harford 
County, Md. Most of the quarry population is congregated along one street, which 
follows the western foot of the ridge. The northeastern part of this street is Delta, 
Pa. ; the southwestern is Cardiff, Md. 
For the literature of Peach Bottom slate the reader is referred to the writings <>i 
Rogers, Lesley, Frazer, AVilliams, Mathews, Merrill, and Merriman. 6 
The slate belt has on its northwest side a sericite-chlorite-quartz-schist (con- 
taining rounded grains of zircon), with a foliation striking N. 45° E. and dipping- 
southeast at an angle of 75°. About midway between Delta and Bryansville this 
schist is calcareous. According to the reports of the Second Pennsylvania Survey sine 
ilar schists recur on the southeastern side of the slate belt, and the whole schist forma- 
tion overlies in synclinal structure the older gneisses and serpentines which occur on 
either side of it; and these schists and the associated slate are classified as Cambrian, 
although no typical Cambrian fossils have as yet been found in them. There is a 
good exposure of the relations of the slate to the rocks on the southeast (referred to 
;by Rogers) on the east side of Slate Point on the towpath along the Susquehanna. 
The slate here conformably underlies about 50 feet of slightly muscovitic quartzite, 
which was formerly quarried for canal construction, both rocks striking N. 45°-50° 
E., and dipping southeast at 70°. A little farther east this quartzite is followed by 
a coarsely plicated gneiss consisting of quartz, plagioclase, muscovite, hornblende, 
and epidote, and having the same strike and dip. Still farther east, nearly a quarter 
of a mile from the contact of the slate and quartzite, about 70 feet of slightly musco- 
ntic quartzite crop out with a strike of N. 45°-50° E., dip 42° SE., and are fol- 
lowed conformably by a gneiss like that previously described. These quartzites and 
1 a Rogers, H. D., Geol. Pennsylvania, 1858; Frazer, Persifor, jr., York and Lancaster comity sheets, 
Second Geol. Survev. Pennsylvania, Vol. CCC, Atlas, 1878,1879; Mathews, E. B., Maryland Geol. Sur- 
rey, vol. 2, PI. XXX, 1898. 
i : b Rogers, H. D., Geol. Pennsylvania, vol. 1, 1858, pp. 188, 189; Frazer, Persifor, jr., Geol. Lancaster 
Jountv, Second Geol. Survey Pennsylvania, Vol. CCC, 1880, pp. 179-190, and Pis. VII, VIII: Williams, 
x. H., The petrography and structure of the Piedmont Plateau: Bull. Geol. Soc. Am. vol. 2, 1891, p. 
;04; Lesley, J. P., Second Geol. Survey Pennsylvania, Final Rept. vol. 1, 1892, pp. 136-141; Mathews, 
5. B., Maryland Geol. Survev, vol. 2, 1898, pp. 215-231, 239-241; Merrill, G. P., Treatise on rocks, rock 
veathering and soils, 1897, p.* 229; also Stones for building and decoration, 3d ed., 1903; Merriman, M .. 
The strength and weathering qualities of roofing slates, Trans. Am. Soc. Civ. Engrs., vol. 27, 1892, pp. 
31-349; also vol. 32, 1894, pp. 529-539. 
Bull. 275—06- 
