244 THOMAS C. BROWN 
properly exposed in cross-section, still indicating the wavelike 
flowing motion which brought them into their present position.’ 
ORIGIN OF THE OOLITES 
Odlites are widely distributed in the rocks of this country and 
Europe and are found at many horizons from the Cambrian (or 
even pre-Cambrian)? to the present. They are known to be 
accumulating today at numerous places among which may be 
mentioned certain coral reefs in the open sea, as, for example, those 
around Bermuda and the Bahamas, in Salt Lake, Utah, and in 
certain petrifying springs like those at Carlsbad. 
The odlites of the central Pennsylvania region are somewhat 
variable according to the horizon at which they occur. In the 
Upper Cambrian limestones they are apparently all calcareous, 
elther spherical or oval in shape, composed of concentric layers of 
material generally showing a radial fibrous structure. Between 
crossed nicols some of the spherules show a characteristic dark cross, 
while others have been almost completely transformed into a 
single calcite crystal with twin lamellae distinctly developed. No 
nuclei of foreign material were observed; the fibrous concentric 
structure continued to the center, or the calcite crystal occupied 
this central position with only the marginal fibrous part remaining. 
Associated with these spherical forms were numerous oval and 
rodlike structures having an internal make-up similar to that of 
the odlites. The spherical odlites range in diameter from o. 28 mm. 
too.73 mm. The oval and rodlike grains also show considerable 
variation in size, as these measurements will show: large oval odlite 
grain, long diameter 1.02 mm., short diameter 0.57 mm.; small 
oval grain, long diameter 0.86 mm., short diameter 0.28mm.; long 
rodlike grain, long diameter 2.04 mm., short diameter 0.28 mm. 
The siliceous odlites and the associated calcareous odlites from 
the Ordovician beds are sometimes larger in size. Several measure- 
tT am indebted to Professor A. W. Grabau and Dr. F. F. Hahn of Columbia 
University, who first brought this explanation to my attention. Dr. Hahn has made 
a special study of such motion in stratified deposits. He informs me that in recent 
sediments in the Zuider Zee such a slumping or flowing of the sediments has been 
observed where the slope of the bottom did not exceed four degrees. 
2 See Geikie, Text-Book of Geology, p. 192, footnote. 
