 Since it wasn't his primary task at the Geological Survey, Isachsen did most of his research into the crater question in his own time.He found, when looking at the bed of Esopus Creek, that much of the exposed sandstone and shale showed an unusually closely spaced fracture pattern — every foot (30 cm) instead of every meter (3.3 ft), as is seen elsewhere in the Catskills.He reasoned that if a crater wall lay beneath, the debris from the impact and the sedimentary rock already in the area would have settled more compactly and been more prone to sagging and fracturing over time.