1890 .] 
445 
[Wright. 
satisfied that it was one of these, or at any rate clay of identical 
composition, from which the image was moulded. Under the mi- 
croscope they show precisely the same elements that were detected 
in the image, and they form, when moistened, a plastic material 
that can be moulded. 
The clay-balls are in themselves of much interest as a geological 
phenomenon. The interior of each ball is very different from the 
exterior. The interior is nearly white and very fine-grained, while 
the exterior is covered with coarse sand embedded in rusty-brown 
material. The largest specimen, which was four inches in diame- 
ter, exhibits upon cross section a series of concentric rusty rings, 
from one-eiglith to one-sixteenth of an inch apart, thus showing 
that it is composed of a series of concentric layers and was formed 
upon the concretionary principle, like the nodular iron ore of the 
coal measures. The interior of the balls furnished the finer ele- 
ments of the image, while the coarse quartz grains came from the 
exterior, the two being mixed together in the hands of the artisan. 
The material of the clay balls, when subjected to heat, was found 
to undergo rather complicated changes of color. Moderate heat 
blackens the exterior without greatly changing the interior, as if 
organic matter were present. Stronger heat develops the reddish 
or fulvous color, both internally and externally. Yet, unless the 
strongest heat is at the same time strongly oxidizing, the result 
will be a dark gray. If the flame of a Bunsen gas burner is al- 
lowed to play upon a piece, the portion that was in the centre of 
the flame will be left gray, while only the outer portions will be 
reddened. It is thus very difficult to produce a uniform reddish 
color over the entire surface of a moulded specimen. These facts 
will, I think, account for the different shades of color observable 
upon the surface of the Nampa image, to which previous allusion 
has been made. The dark gray at the end of the shorter leg is 
due to a lack of ox}^gen at the time of burning, and the distribu- 
tion of black and red was due to the inequalities of the flame. 
A DUPLICATE OF THE IMAGE. 
Having proceeded thus far with the investigation, it was natural 
to go a step farther and see if the image could not be reproduced 
in all its essential features. A clay-ball with a liberal coating of 
sand was selected, crushed together in a mortar, moistened into a 
putty and moulded with a knife-blade into some similarity of form 
