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blebby rounded grains


Thin section of Trap from Williamson’s Point, Lancaster Co. Pa. Magnified 400 Diameters.
cropped from page (and surrounding box; faint trace of engraver’s name also lost)
illustrating Persifor Frazer, Jr. (1844-1909). The Geology of Lancaster County. Second Geological Survey of Pennsylvania: Report of Progress in 1877. CCC. Harrisburg, 1880
University of Michigan copy, digitized October 19, 2006

“The rock under the Stanhope lens showed, besides quartz grains, blebby rounded grains of silicates of very minute botryoidal structure along with thin hydro mica scales, which were seen sometimes entirely absent and sometimes in large quantity.”
(p 141)

Frazer’s discussion of observations along a railroad cut through the terrain near the Maryland-Pennsylvania border is forensic in detail and in critical weighing of physical (and visual) evidence.

15 March 2014

botryoidal structure; outcrop geology; interdisciplinarity; forensics; rounds
Percifor Frazer, Geology of Lancaster Country (1877)