The granites sampled by the IDHP have whole-rock Δ18O values of about 7?, which places them at the low end of the range previously observed for granitic rocks that not undergone extensive modification by hot meteoric waters. Over a depth range of 840 m, no significant variation in bulk initial isotopic compositon is observed. All samples have experienced post-crystallization retrograde isotopic exchange among the major minerals (quartz, feldspars, biotite), as is common in plutonic igneous rocks. In the uppermost sample analyzed (only 3m below the Paleozoic sediments), feldspar has undergone exchange with an external reservoir, probably water of meteoric origin, and probably at a temperature near 100¿C.