An area of 8,000 square miles, lying east of the Andes in Ecuador, was explored in 1921. The old Indian towns of Archidona, Tena, and Napo are in the northern part; Macas, the largest settlement in the Oriental region, is at the southern extremity of the area. Astronomical observations were made as a check on the plane-table traverse, which was carried over all routes of travel. Collections of fossils, mostly from the vicinity of Napo, establish one horizon of Turonian (Eagle Ford-Benton) age, and a second of middle Albian (mid-Comanchean) age. Unfossiliferous red beds occur above this Cretaceous section, and below it are sandstones and volcanic rocks. The Napo Cretaceous beds are petroliferous. Cretaceous rocks east of the Andes have been described from Colombia, Venezuela, Peru, Bolivia, and the Argentine Republic, but this is the first description of such rocks from eastern Ecuador.