Description of the Geology of
Adams County
Pennsylvania

 
Adams.- Area, 530 square miles; population in 1880, 32,455. Two thirds of the county consists of mesozoic soft sandstone and shale, traversed by extensive trap-dykes. Its western townships rise upon the South mountain massif of Azoic rocks, resembling the Huronian series in Canada, very siliceous and porphyritic, carrying some copper ores, as yet unproductive. The York county limestone belt of the Codorus valley spreads over Conowago township and parts of Oxford and Union, as far as Littlestown, and is bordered on the south-east by the mica-schist belt; the chlorite-schist belt just enters the south-east corner of the county. Extensive out-crop fragments of quartzite indicate the presence of the Potsdam sandstone No. I in Berwick township, along the continuation of the Pigeon hills of York county; and several thousand feet of rocks assignable to No. I make up the mountain ridges of Menallen and Franklin townships, north of the Chambersburg turnpike. The county is wholly agricultural; the inhabitants are descendants of early German settlers; and on the trap hills overlooking its seat of justice, Gettysburg, was fought the decisive battle of the Civil War in 1863. (See Report C.) 

From: A geological hand atlas of the sixty-seven counties of Pennsylvania :embodying the results of the field work of the survey, from 1874 to 1884. By J. P. Lesley. (Report of progress (Geological Survey of Pennsylvania), v. X ) Harrisburg, PA : Board of commissioners for the second geological survey, 1885.

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