Second Pennsylvania Geological Survey Maps
1893 Geologic Map of Pennsylvania
The 1893 geologic map of Pennsylvania was the culmination of the tremendous scientific accomplishments of the Second Pennsylvania Geological Survey under the direction of J. Peter Lesley, State Geologist. It was based on earlier published Survey maps and other miscellaneous maps, which are listed in the title block of the map plate. Perhaps most notably, the map used information from county geologic maps that were published by the Survey from 1874 to 1892 at a scale of 1 inch = 2 miles (approximately 1:125,000). The 1893 geologic map, which is credited to A. DW. Smith, Assistant Geologist, was issued as part of an atlas that accompanied the final report of the Second Survey. 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 establishment of the First Pennsylvania Geological Survey.
The 1893 state geologic map was photolithographed and printed by Julien Bien & Co., New York City, on four sheets at a scale of 1 inch = 6 miles (1:380,160). The PDF version in the downloadable ZIP file was created from a scan of 24 individual sections of the map that long ago had been mounted on one piece of canvas.
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.”