On Chemical Composition of Dciemonelix 



thickness, in the lower part of a large horizontal trunk of a 

 corkscrew, Avithin a foot of the present surface. This specimen 

 answers exactly to the excellent description quoted above. The 

 dendritic portions perfectly i-esemble moss-agates, except for 

 the pink and red tints. 



No. II. occurred as a large irregular mass five or six inches 



across, and about 

 two inches thick, 

 near the top of a 

 spiral, within six 

 inches of the sur- 

 face. In color it is 

 creamy white, with 

 a few minute specks 

 of black manganese 

 dioxide. In , t ac- 

 ture some parts are 

 granular, other parts 

 ^ are dense and gela- 

 tinous, like hard 

 wax. This speci- 

 men, being near the 

 Fig. 3 surface, was partly 



dehydrated. 



No. III. occurred 



Fiff. 3. — "Twin Sciews" sei'Ured for 1he Morrill Geo- 

 logical Expedition of ISSIn, by Mr. Geoi«e \{. Wielanii, near 

 Squiiw Canyon, Sioux County, Nebraska. A and 15 are sec- 

 tions from the fossil at the points A and B respe(:tively, 



showing the prreat tubes filled with silicic acid. Ana'ysisIII. j.- 1 T 



was made from material obtained from tubes at ('. Height aS a Vertical CyilU" 

 of spirals about 1.1 meters (1 fr. 4 in). Length of "rhizome" 

 2.77 meters (; ft.); diameter of " rhizome" 25 cm. (10 in.). drical tube one and 



a half inches in diameter, several inches long, at the lower end of 

 the axis of a spiral, three feet below the surface. In color it 

 is creamy white, with green tints, and quite translucent. 



No. IV. Portions of a tube about three-eighths inch in di- 

 ameter, about a foot long, taken from a weathered-out trunk of 

 a corkscrew on the surface of the ground. Color, white. 



The hardness of this material varies greatly. The fully 



127 



