The rocks of the Guadalupe group, as described by Tarr,3 Richardson,4 Girty,5 and others, occupy the Guadalupe Mountains, in the northern part of Culberson County, Texas. They extend northward far across New Mexico, where, on account of difference in fauna and lithology, Darton6 has termed them the Chupadera formation. This correlation was indicated by the apparent continuity of the outcrops in the great mountain range, as previously noted by Richardson, Girty, and others. However, as there were possibilities of overlaps and separating faults, further study of the supposed continuity seemed desirable. With this purpose we spent part of the early summer of 1925 in an examination of the range in southern Eddy County, New Mexico, and its continuation into Texas. Fossils were collected at many points, and they have been studied by Dr. G. H. Girty as to their bearing on the correlation of the various beds and to . . .