ABSTRACT
One can approach diagnosis of the climatic regimes of past epochs either by theoretical constructions based on physical and dynamical laws, using little more than an outline knowledge of the dispositions of land and sea and mountain ranges and any necessary allowance for differences of heat flux at earlier stages of the history of Earth and sun, or from observation of the traces left by former climates in the fossil record. These may, rather loosely, be called the theoretical and the empirical approach respectively. Certainty and understanding only begin to appear when, and in so far as, these two approaches can be seen to verify each other and help sort out the evidence.
