Abstract Field geologists and explorationists are of necessity immersed in numerous very detailed surface and subsurface observations. They are often perplexed by the choice of relatively simple geophysical models that so elegantly explain the origin and evolution of sedimentary basins. Geophysicists, on the other hand, search for a simple theme to explain the origin of sedimentary basins and, much like managers, are often impatient with lengthy detailed geological discourse that often uses fancy jargon to hide the very real difficulty that geologists have in separating important evidence from mere encyclopaedic description. The following musings address the quality and limitations of geologic and geophysical evidence that may be used to evaluate the relative roles of stress, thermal effects and gravity loading, which have been so lucidly summarized by M. H. P. Bott in the preceding summary. The fine papers presented during this meeting, of course, have led to significant modifications of some of my earlier thoughts. Because these have been previously published elsewhere (Bally & Snelson 1980; Bally 1980), they are summarized here only for the convenience of the reader.