The Baltimore Mafic Complex is here revised and divided into four newly named formations: the Hollofield Layered Ultramafite and Mount Washington Amphibolite of the Laurel belt and the Raspeburg Amphibolite and Bradshaw Layered Amphibolite of the Bel Air belt. The name Hollofield is proposed for layered rocks exposed at the abandoned Hollofield quarry and described in detail by Hopson (1964). The unit consists of interlayered ultramafic and mafic rocks. Layers range in thickness from a few centimeters to tens of meters. Actinofels and actinoschist are predominant and very often appear as green tangled masses of fine actinolite needles. One third of the formation is composed of amphibolite, either actinolitic or hornblendic. Serpentinite is also a common rock type. Unit is in thrust-fault contact with the Loch Raven Schist, Oella, and Sykesville Formations of the Wissahickon Group. Underlies Mount Washington Amphibolite in an east-west anticline, which is truncated on the southeast by the James River Formation. Age is Cambrian(?).

Source: GNU records (USGS DDS-6; Reston GNULEX).