Precambrian Quartzo - Feldspathic Gneiss from the Herman

Precambrian quartzo-feldspathic gneiss was encountered at an elevation of —3616 feet in the Herman 1A well drilled in southeastern Erie County, Ohio, by the Amerada Petroleum Corporation. The five samples of this gneiss that were studied exhibit varying degrees of gneissose foliation. In order of decreasing abundance, microcline, plagioclase, quartz, and biotite together account for an average of 75% of the mineralogy. Greenish saussuritized plagioclase in layers and veins is abundant in three of the samples. Based on the presence of minor amounts of garnet, a plagioclase composition of An36, and the location of the well, the gneiss is considered to lie within the Grenville orogenic belt of high-grade, regionally metamorphosed rock.