The following notes concerning the general geology of the Front Ranges of the Andes between 18 degrees and 23 degrees south latitude were obtained during a rapid reconnaissance made in January and February, 1920. They are published through the courtesy of Richmond Levering and Company, for whom the geological examinations were made. Very few geological data are available concerning this little-known region, so that it is hoped the material presented here will be of interest and value in spite of the many obvious deficiencies, which in part resulted from the rapidity with which the field observations had to be made.
S. C. Herold (1920)2 has recently summarized the scattered literature pertaining to the southern half of the area under discussion. The data which he presents will not be recounted here, as his paper is accessible to all geologists. In March, 1922, while this manuscript was receiving its final revision . . .