Name Rush Brook Member of Loch Raven Schist (new) is proposed for quartz-rich gneiss and schist that outcrop along Rush Brook in Baltimore Co., MD. The member is heterogeneous, but generally quartz-rich and fine-grained. Most typical rock types are interlayered biotite-feldspar-quartz gneiss, biotite-feldspar quartz schist, and muscovite-biotite-feldspar-quartz schist. Interlayered medium-grained quartzites are locally important. Unit also contains amphibolite and marble. Tourmaline is common accessory mineral in schist-quartzite assemblage. Thickness ranges from 0 to 600 m. Overlies Cockeysville Marble; underlies main body of Loch Raven Schist of Wissahickon Group. Age of entire Wissahickon is given as Cambrian-Ordovician(?).
Source: GNU records (USGS DDS-6; Reston GNULEX).
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