266 ELWOOD S. MOORE 
and has not been observed in place. I do not think there is much 
to justify his theory, as there is no evidence of igneous activity 
anywhere in the vicinity nor other geological features to suggest the 
presence of hot springs. 
The other theory, and the only reasonable one to my mind, is 
that they originated by the replacement of limestone. This 
Fic. 5 —Photomicrograph of calcareous odlites in various stages of alteration to 
siliceous odlites. X45. 
explanation was suggested by Barbour and Torrey who made 
some microscopical examinations and chemical analyses of these 
rocks without seeing them in the field.‘ The following analyses 
were made by these men and show a variation in composition from 
1“ Notes on the Microscopical Structure of Odlites with Analyses,” Am. Jour. 
Sci., 3d ser., XL (1890), 246-40. 
