Through the courtesy of Professor J. W. Spencer, I haveX received an early copy of his paper on the “ Great Changes ofLevelinMexico and the Interoceanic Connections,“' containing theobservations and conclusions derived from a visit paid to this regionin 1895, with the special object of determining on the spot whetherthe suggestion that the drainage of what is now the Gulf of Mexicoformerly crossed the Tehuantepec Isthmus into the Pacific.