Stereo-derived topographic profiles across furrows in the ancient (~4 Gyr) dark terrain of Galileo Regio, Ganymede, suggest flexural uplift. Modeling of the rift-flank profiles implies an effective elastic thickness of ≈0.5 km, heat fluxes in the range 60--80 mW m-2 at the time of deformation, and a brittle-ductile transition depth of 2--3 km. The elastic thicknesses are comparable to estimates for grooved terrain on Ganymede, and chaos regions on Europa, and may be characteristic of the point during cooling at which the available stresses can no longer cause significant ice shell deformation. The furrowed dark terrain heat fluxes exceed likely chondritic values, and are plausibly a result of early cooling of Ganymede following accretion. Non-synchronous rotation may have contributed to the 2--3 MPa stresses required to cause the observed deformation.