apropos of nothing, the historical records of the Shang dynasty are largely divinations recorded on tortoise shells. some of them are even further annotated retrospectively about the outcome, though as you'd expect, most of the annotations were accomodating (e.g. "rain next week. rain came in two weeks. auspicious."). some of them were negative, though. incidentally, the record gives at least a rough idea of the growing season, and thus the climate at the time. i'm greatly oversimplifying here, see e.g. http://en.wikipedia.org/wiki/Oracle_bone
self-interest: does anyone know of a resource documenting recovered tortoise plastrons in detail? it seems like there could be an interesting statistical analysis. i've only read the summary in Sources of Chinese Tradition, vol. 1 (highly recommended).