262 ELWOOD S. MOORE 
The most interesting concretions in this area are, however, 
the calcareous and siliceous odlites. 
CALCAREOUS AND SILICEOUS OOLITES 
Calcareous oélites are of such common occurrence that they 
require but a brief description here. Several beds of them occur 
Fic. 2.—Photomicrograph of a calcareous oélite with sand grain as nucleus. 45 
in the transition series in the vicinity of State College and in lime- 
stone which has been largely recrystallized. They vary in size 
from 1.35 mm., the largest measured, to 0.22 mm. in diameter. 
They have not been seen in the very fine-grained limestone of the 
series. Their presence in thin sections is often indicated by a single 
outer circle but at other times the concretion consists of several 
concentric spheres. There is generally a nucleus of some sort in 
