The Peruvian Cordillera offers a field for geologic research so vast that in spite of the work of many investigators it still possesses the allurement of an almost virgin country. The present conception of the regional geology has of necessity been built up from scattered information rather than from comprehensive surveys, and its accuracy obviously depends upon the degree to which the studies that have been made afford a fair sample of the many features of the Cordillera. The published works of Raimondi, Bravo, Steinmann, Lisson, Bowman, and others and the many papers that have appeared in the bulletins of Peruvian organizations have already provided an excellent fund of information and a basis for further advancement; but the area to be studied is so great that all existing work hardly amounts to more than a very partial examination. The stock of available knowledge still needs to be strengthened . . .