Second Pennsylvania Geological Survey Maps
1893 Geologic Map of Pennsylvania
The 1893 geologic map of Pennsylvania was the culmination of the tremendous accomplishments of the Second Pennsylvania Geological Survey. The geologic map was based on county geologic maps that were published from 1874 to 1892 at a scale of 1 inch = 2 miles (approximately 1:125,000). The map was released under the direction of J. Peter Lesley, State Geologist. More information on the Second Pennsylvania Geological Survey can be found in the February 1987 issue of Pennsylvania Geology (v. 18, no. 1), which commemorated the sesquicentennial year of the Survey.
County Geologic Maps
Second Geological Survey geologic maps for all of the state’s counties were also published in an atlas at a smaller scale of 1 inch = 6 miles (1:380,160): J. P. Lesley, 1885, 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, Report of Progress X, Harrisburg, Pa., Board of commissioners for the Second Geological Survey. This volume includes “a short account of the characteristic features of each county” (p. xii, et seq.) and is available from the Pennsylvania State University Libraries.
The geologic cross section below is also from the atlas (p. vi). It shows the geographical trace of units labeled II, III, IV, V, VIII, IX, and XIII. These units are described under “Short explanation of the geological structure of Pennsylvania” (p. vii). The geographic landmarks as written on the cross section include: “Coal Measures XIII, Allegheny mountain, Terrace of Catskill, Bald Eagle mtn., Nittany or Sinking Valley, Canoe mtn. synclinal, Canoe valley, Tussey mountain, Warrior’s ridge, Huntingdon, Terrace mountain (Broad Top synclinal), and Jack's mtn. anticlinal.” The cross section includes a measure of the thickness of the “arch” as five miles, showing that these mountains, as J. P. Lesley put it, “stood as high above the sea as do the Alps, Andes, and Himalaya mountains of today.”