THOMAS. } ANCIENT WORKS, ALLAMAKEE COUNTY, IOWA. 27 
235 feet; the entire outer circumference is 807 feet, the length of the 
portion along the bluff 100 feet, and of the overlapping portion at the 
entrance 45 feet. The wall is quite uniform in size, about 4 feet high 
and from 25 to 27 in width, except along the bluff, where it is scarcely 
apparent; the entrance is 16 feet wide, and the ditch 5 to 6 feet wide 
and 3 feet deep. On the north, adjoining the wall on the outside and 
extending along it for about 100 feet, is an excavation (c, Plate II) 35 feet 
wide at the widest point and 3 feet deep. 
As this ground, including the circle, has been under cultivation for fif- 
teen years, it would be supposed the height of the wall is considerably 
less than it originally was, but this is probably a mistake. On the con- 
trary, if was originally probably but 20 feet wide and not more than 3 
feet high, composed mainly of yellowish brown clay obtained, in part at 
least, from the ditch, but during oeeupaney the accumulation of count- 
less bones of animals used as food, stone chips, river shells, broken pot- 
tery, and dirt, and, since abandonment, the accumulation of sand drifted 
by the winds from the crumbling sandstone butte (C, Plate I) over- 
looking it, have not only filled the ditch but elevated the wall and 
whole interior area 2 feet or more. This accumulation of sand is so 
great and so uniform over the plateau that fifteen years of cultivation 
have not sufficed to reach the clay of the original surface nor to unearth 
or even penetrate to the bones, pottery fragments, and other refuse 
matter covering the original surface in the circle. 
Trenches cut across the wall at various points indicate, first, a layer of 
sand about 1 foot thick; immediately below this an accumulation of 
refuse matter forming a layer from 1 to 2 feet thick; under which was 
the original clay embankment 2 feet thick, resting on the natural surface 
of the ground. A section of the ditch, embankment, and excavation 
is shown in Plate II. The dotted line a b indicates the natural surface ; 
No. 1 the original clay layer of the wall; No. 2 the layer of earth and 
refuse material with which the ditch is filled; and No. 3 the top layer 
of sand. 
In No. 2 were found charcoal, ashes, fragments of pottery, fractured 
bones, ete. 
A broad belt of the inner area on the east side was explored, and the 
same conditions were found to exist here as were revealed by the trenches 
across the wall and ditch, except that here the shells were more abun- 
dant in layer No. 2, and there were many burnt stones. 
On the southeastern portion of the plateau (B, Plate I) are six nearly 
parallel lines of mounds running northeast and southwest, mostly cir- 
cular in form, varying from 15 to 40 feet in diameter, and from 2 to 
6 feet in height; a few, as indicated in the figure, are oblong, varying 
in length from 50 to 100 feet. The number in the group exceeds one 
hundred. 
While engaged in excavating these mounds Colonel Norris observed 
anumber of patches of the level area quite destitute of vegetation. The 
