MAINE MARYLAND. 67 
and the section photographed in PL XI, A came from that piece. The Brownville 
slate is highly crystalline. 
Forks, Somerset County. — A slate prospect opened in this town in 1890 was visited 
by the writer in 1905. a 
This prospect is about 18 miles west of the North Blanchard quarries, in the s< >uth- 
west corner of the town of Forks, about 3 miles northeast of Caratunk, and about a 
mile northwest of Pleasant Pond. It is on Holly Brook, on land owned by Lawrence 
Hill. The nearest railroad is the Somerset Railway extension at Mosquito Narrows, 
6 miles distant. 
The cleavage strikes N. 55° E. and dips from 90° to steep northwest and southeast, 
owing to minor folding. The bedding is probably not far different. 
The slate is bluish black, of fine texture and cleavage surface, with a luster not so 
great as that of the Brownville slate. It is graphitic, contains a very small amount 
of magnetite, has no argillaceous odor, does not effervesce in cold dilute hydrochloric 
acid, is sonorous, splits, and can be perforated readily. Neither the ledge nor the 
fragments, said to have been exposed fifteen years, show discoloration. 
Under the microscope the section shows a matrix of muscovite (sericite), with a 
brilliant aggregate polarization, proving it to be a mica slate. The cleavage is fine 
and regular. There are about 52 lenses of pyrite to each square millimeter, measur- 
ing (in transverse section) from 0.02 to 0.06 mm. in length by from 0.004 to 0.016 
mm. in width. In sections parallel to the cleavage these lenses have a very irregu- 
lar outline and are often as broad as long. These lenses account for the limonitic 
staining on cleavage surfaces of water-soaked specimens. Quartz is abundant but 
minute. No carbonate was detected. A few tourmaline prisms up to 0.11 mm. in 
length. Some scales of chlorite with interleaved muscovite measure up to 0.09 mm. 
There are rare zircon fragments and aggregations of rutile crystals. 
The constituents of this slate, arranged in descending order of abundance, appear 
to be muscovite, quartz, chlorite, pyrite, and graphite, with accessory tourmaline, 
zircon, and rutile. 
This Pleasant Pond slate differs from the Monson slates in having a lustrous and 
smooth surface, and from the Brownville slate in having much less magnetite and a 
little less luster. It would prove suitable for roofing or mill stock purposes. 
Whether, like the other slates of this State, it is interbedded with quartzite at fre- 
quent intervals could not be determined. 
The more important features of Maine slates as brought out in the above descrip- 
tions will be found set forth in tabular form opposite page 124. 
MARYLAND. 
By T. Nelson Dale. 
The slate of Cardiff, in Harford County, about 30 miles northeast of Baltimore, 
extends up into Pennsylvania, and will therefore be considered under a heading of 
its own (see pp. 85-88). Slate occurs also in Montgomery and Frederick counties, 
about 40 miles west of Baltimore and 33 miles northwest of Washington, where ifc 
has been prospected and quarried to a small extent (see map forming rig. 5). 
Geological relations.— For the geology of the region the reader is referred to the 
writings of Williams, Keyes, and Mathews. & Keyes's section passes through Sugar- 
loaf Mountain and along the Baltimore and Ohio (Metropolitan Branch) Railroad to 
a See note on a new variety of Maine slate in Bull. U. S. Geol. Survey No. 285. 
f> Williams, G. H., The petrography and structure of the Piedmont Plateau in Maryland: Bull. Geol. 
Soc. Am., vol. 2, 1891, pp. 301-318, and map, PI. XII. Keyes, C. R., A geological section across the 
Piedmont Plateau in Maryland: Bull. Geol. Soc. Am., vol. 2, 1891, pp. 319, 322, and section fig. 3. 
Mathews, E. B., On Iiamsville slate: Maryland Geol. Surve v vol. 2, 1898, pp. 231-232, and map, 
PI. XXX. 
