BY FRED E. WRIGHT
Experimentation has long been employed in geology as an indirect means of approaching the solution of certain problems by a process of analogy; such initiative experiments have met, however, with only a moderate degree of success, and in recent years have been largely replaced by direct measurements on reproducible systems of definite composition subjected to known conditions of temperature and pressure. This change in mode of attack has been made possible by the rapid development, during the past three or four decades, of physics and chemistry; this in turn has led to a better appreciation of the fundamental principles involved in many geological problems and has placed at the disposal of the geologist methods of attack which enable him to solve problems hitherto deemed beyond the range of experiment. This part of geology is not . . .