Heat flow, in situ stress, in situ S wave and P wave velocities, and in situ density from borehole gravity were successfully measured in a 5.3-km-deep borehole in the Michigan basin. Precambrian (?) red beds and two altered basic igneous bodies were encountered beneath the known Cambrian succession of the basin. Petrological and paleomagnetic studies were undertaken on oriented samples obtained from the igneous body at the base of the hole and on other samples. The igneous body appears to have undergone greenschist metamorphism, probably about 600--800 m.y. ago. The red beds are correlated with the Keweenawan 'series' of northern Michigan on the basis of paleomagnetism and lithology. No evidence was found of a post-Cambrian heating event which might be expected if thermal contraction had caused basin subsidence in a manner analogous to the subsidence of the midoceanic ridges.