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
a race connection or a similarity in culture between the
mound-builders and the pueblo Indians, see Dawson, _Fossil
Men_, p. 55; Foster, _Prehistoric Races of the United States_,
Chicago, 1873, chaps. iii., v.-x.; Sir Daniel Wilson,
_Pre