THEN AND NOW GEOLOGIC INVESTIGATIONS OF FLORENCE BASCOM, GEORGE W. STOSE AND ANNA JONAS STOSE IN SOUTHEASTERN PENNSYLVANIA

Florence Bascom (1862-1945), George Willis Stose (1869-1960) and Anna Jonas Stose (1881-1974) became the most recognized geologic field mapping team in southeastern Pennsylvania. George began his investigations in the Appalachian Mountain region and Adams County, Pennsylvania in the early 1900s, working with legendary geologist Florence Bascom. Florence taught at Bryn Mawr College near Philadelphia and conducted the initial research on the age and structure of the Piedmont metamorphic rocks, especially the Wissahickon Formation. In the 1920s, George teamed up with Anna Jonas, a student of Florence Bascom. George and Anna married in 1938. This team mapped individual quadrangles and regions in York and Lancaster counties. Their reports became foundations for future investigations. Working with limited exposures and no knowledge of plate tectonics, they made very detailed interpretations of the stratigraphy and structure. With modern mapping techniques and more rock exposures, just how well have the Bascom and Stose ideas stood the test of time? Examples from five of their reports are examined, including then-and-now photographs and diagrams. Reports include the Crystalline Rocks of Cecil County, Maryland (including southern Lancaster County) by Bascom, and Lancaster 15’ Quadrangle (1930), New Holland 15’ Quadrangle (1926), Middletown 15’ Quadrangle (1933) and Geology of the York-Hanover District (1944) all by Stose and Anna Jonas Stose.