SILICEOUS OOLITES IN PENNSYLVANIA 263 
the center of the concretion. This is frequently a sand grain and 
grains have been found varying from 0.6mm. to 0.04 mm. in 
diameter and it is believed that some small body has in all cases 
served asa nucleus. Ina few cases what appear to be recrystallized 
fragments of limestone serve as a central body. 
The occurrence of these concretions is believed to be due to the 
intermixture of sand grains and calcium carbonate. The fact that 
limestone-conglomerate beds are associated with these rocks sug- 
gests that the sea was near the critical level in this area, and portions 
of limestone, probably not thoroughly consolidated, were from 
time to time exposed to erosion by fresh water or broken up by 
shore waves, resulting in the supersaturation of the sea water with 
calcium carbonate and the deposition of odlitic limstone near the 
shore. Beds of well-rounded sand grains underlying the odlite 
beds suggest further a sea advancing upon deposits of wind-blown 
sand mixed with a certain amount of limestone. : 
Although siliceous odlite has been reported as occurring in 
Missouri and Tennessee, it is not a common type of rock in this 
country. The area in Pennsylvania has therefore been a notable 
one, although never thoroughly described. Dr. G. R. Wieland 
wrote a brief description of the rock and as a result it has locally 
been known as Wielandite and sold by some mineral dealers under 
that name.* 
The area in which it occurs in large quantity covers about forty 
square miles and it is scattered sparingly over a much larger area. 
It has been reported from the Chambersburg, Pa., area about 
seventy-five miles south of State College and in rocks of similar 
age and physical character.?. The rock occurs in large quantities 
as broken fragments on the surface and in the form of larger con- 
cretionary masses of chert. There are as many as six beds of the 
rock lying one above the other in the limestone, from five to twenty 
feet apart. The beds are generally thin, varying from an inch to 
twenty inches in thickness, and often extremely irregular. The 
oolites are often nearly white in a dark matrix and almost black in 
a light-colored matrix. They consist of chert or flint and when 
I Diep: Jour. Sci., 4th ser., IV (1897), 262. 
2 U.S.G.S., Folio 170. 
