34 The American Naturalist. [January, 
General Notes. 
GEOLOGY AND PALEONTOLOGY. 
On the Formation of Oolite.—Dr. A. Rothpletz has proposed 
a theory of the formation of odlite, which is as interesting as it is 
novel. He noticed on the shores of Great Salt Lake, Utah, snow-white 
and silver-gray calcareous corpuscles in great numbers. They form @ 
large part of the beach sand, and where they lie in the water they are 
partly covered with a bluish-green alga-mass. On examination the 
algoid bodies proved to be colonies of cells of the lime secreting alge, 
Gleocapsa and Gleothece. By a series of experiments Dr. Rothpletz 
satisfied himself that the calcareous bodies secreted by the plants and 
the calcareous bodies which compose the beach sand are identical. 
Pursuing his researches, the author investigated the odlites from the 
strand of the Red Sea, and found that although slightly differing m. 
structure, these odlites originate similarly to those of Salt Lake; that 
is, from lime secreting algæ. 
In studying fossil forms Dr. Rothpletz has found in a gray limestone 
from the Lias of the Vilser Alps, and in the great oölite structure of 
gated by Wethered, and more recently by Bleicher (May, 1892), 
closely resembles that of the Red Sea odlite. In view of these 
Dr. Rothpletz is inclined to believe that at least the majority of the 
marine cal¢areous odlites with regular zonal and radial structures are 
of plant origin; the product of microscopically small alge of very 
low rank, capable of secreting lime—From Botanisches Centralbla 
Translated by F. W. Cragin for the American Geologist, Nov., 1892 
intended as a basis for the economic geology of that region, and 1 
therefore, general rather than special and detailed. ‘The rocks of the 
*Report on Geology of Northeastern Alabama and adjacent portions of Georgis 
d Tennessee. Bulletin No. 4, Geological Survey of Alabama. By C. Wil 
Hayes, Assistant Geologist U. S. Geol. Surv., 1892. 
