264 ELWOOD S. MOORE 
polished some specimens make attractive ornaments. ‘The solid 
odlite rock may grade over into chert with few odlites, and further, 
to solid chert. The odlites frequently occur in concretions of chert, 
thus showing a mass of small concretions forming a larger one. 
A complete sand grain often forms the nucleus of these con- 
cretions but frequently the sand grain is partially or wholly granu- 
Fic. 3.—Photomicrograph of a siliceous odlite with a sand grain as nucleus. X35 
lated just as quartz grains are in highly metamorphosed rocks, 
and it is difficult to explain how these could be broken by compres- 
sion without deforming the concretion, which often remains per- 
fectly round, unless a recrystallization of the odlite as a whole 
has occurred. In the ability of concretions to reform and recrystal- 
lize under metamorphic conditions, as well as in the marked simi- 
larity which concretions of any mineral possess in widely separated 
regions they show a striking similarity to crystals. While so far as 
