File:Bulletin 426 Plate IV A Gaithers Granite Quarry.jpg

English: Plate IV A Original caption: "Gaither's Granite Quarry, Ellicott City, Maryland."

Text from the volume referring to the figure:
Several quarries opened in the steep and moderately high granite cliffs along the east side of Patapsco River have been operated nearly opposite Ellicott City. The largest of these, known as the Gaither quarry, comprises two large openings that adjoin each other and have been worked back from the river into the granite cliffs, with an elevation from the base to the top of about 75 feet. (See Pl. IV, A.) The rock is a biotite granite of medium dark blue-gray color and medium grain. Its structure is decidedly foliated or schistose, though much less pronouncedly so than that of the granite gneiss at Port Deposit and Frenchtown; and its original granite characters are still apparent. Hand specimens of the granite show abundant fine granules of yellow epidote closely associated with the biotite. Irregular grains of brownish allanite are also apparent in the hand specimens. Because of its richness in epidote and allanite Keyes classified this granite and some of the granites from the Port Deposit, Woodstock, Dorseys Run, and Ilchester localities as allanite-epidotebearing granites.

The granite consists of soda-lime feldspar (oligoclase), potash feldspars (orthoclase and microcline), quartz, and biotite, together with accessory zircon, apatite, hornblende, allanite, epidote, and secondary chlorite and epidote. Intergrowths of the feldspar and quartz in more or less rounded grains are of common occurrence. The feldspar is partly cloudy and opaque from alteration, and the larger individuals inclose small rounded grains of feldspar and quartz. Allanite and epidote occur as parallel growths. Partial granulation of the quartz and feldspar into fine mosaics from pressure metamorphism is pronounced.