practised irrigation (which would not be required in the Mississippi valley) or used adobe-brick, yet Mr. Morgan was inclined to admit them into his middle status of barbarism because of the copper hatchets and chisels found in some of the mounds, and because of the apparent superiority in horticulture and the increased reliance upon it. He suggested that a people somewhat like the Zunis might have migrated eastward and modified their building habits to suit the altered conditions of the Mississippi valley, where they dwelt for several centuries, until at last, for some unknown reason, they retired to the Rocky Mountain region. It seems to me that an opinion just the reverse of Mr. Morgan's would be more easily defensible,--namely, that the ancestors of the pueblo Indians were a people of building habits somewhat similar to the Mandans, and that their habits became modified in adaptation to a country which demanded careful irrigation and supplied adobe-clay in abundance. If ever they built any of the mounds in the Mississippi valley, I should be disposed to place their mound-building period before their pueblo period. [Footnote 155: For original researches in the mounds one cannot do better than consult the following papers in the _Reports of the Bureau of Ethnology_:--1. by W. H. Holmes, "Art in Shell of the Ancient Americans," ii. 181-305; "The Ancient Pottery of the Mississippi Valley," iv. 365-436; "Prehistoric Textile Fabrics of the United States," iii. 397-431; followed by an illustrated catalogue of objects collected chiefly from mounds, iii. 433-515;--2. H. W. Henshaw, "Animal Carvings from the Mounds of the Mississippi Valley," ii. 121-166;--3. Cyrus Thomas, "Burial Mounds of the Northern Section of the United States," v. 7-119; also three of the Bureau's "Bulletins" by Dr. Thomas, "The Problem of the Ohio Mounds," "The Circular, Square, and Octagonal Earthworks of Ohio," and "Work in Mound Exploration of the Bureau of Ethnology;" also two articles by Dr. Thomas in the _Magazine of American History_:--"The Houses of the Mound-Builders," xi. 110-115; "Indian Tribes in Prehistoric Times," xx. 193-201. See also Horatio Hale, "Indian Migrations," in _American Antiquarian_, v. 18-28, 108-124; M. F. Force, _To What Race did the Mound-Builders belong?_ Cincinnati, 1875; Lucien Carr, _Mounds of the Mississippi Valley historically considered_, 1883; Nadaillac's _Prehistoric America_, ed. W. H. Dall, chaps. iii., iv. The earliest work of fundamental importance on the subject was Squier's _Ancient Monuments of the Mississippi Valley_, Philadelphia, 1848, being the first volume of the Smithsonian Contributions to Knowledge.--For statements of the theory which presumes either