under horizontal thrusts becomes more and more advanced. This is consistent with the observed diminution of the differences in the carbonization of coals lying at different depths in the vertical column as the regional carbonization passes through the semibituminous and anthracite ranks. Since neither the relative values of the factors, pressure, temperature and time, or their respective substitutional values in the different cases, are known, and since the organic deposit itself consists of mixtures of compounds, many of which are undetermined as also are many of the chemical changes ensuing, any attempt at an empirical formula of meta-morphism is purely speculative. "Normal" regional temperature probably is of little value, though temperatures generated under thrust gain importance as the thrusting becomes more intense. The product of thrust into competency becomes of paramount importance, both directly and indirectly, as the alteration progresses.