THE ORIGIN OF CERTAIN PALEOZOIC SEDIMENTS 247 
concerning the origin of odlites.' He proved that in every recent 
occurrence of odlite of which he was able to obtain samples, the 
odlite grains consist of the mineral aragonite, while in the older 
or fossil types they consist of calcite. He concludes that all 
odlites were originally formed as aragonite and later changed to the 
more stable mineral form calcite. But aragonite cannot form under 
any ordinary marine- or fresh-water conditions due to simple 
concentration of the solution of calcium bicarbonate. There are 
then two possible conditions under which the aragonite odlites 
might have accumulated. They might be the products of organic 
activity, for it is known that both animals and plants have the power 
to abstract calcium carbonate from the water and build it up into 
their skeletons in the form of aragonite. The skeletons of many 
of the coralline algae, for example, are formed in this way. The 
odlite grains might also be produced by direct chemical precipita- 
tion due to some special precipitating agent. By experimental 
research Linck found that, under ordinary conditions of tempera- 
ture, the calcium carbonate would be precipitated from the calcium 
sulphate of sea water by the addition of sodium carbonate or 
ammonium carbonate. When so precipitated it assumed the 
mineral form aragonite. As a result of his investigations he con- 
cluded that although the solution of calcium carbonate (bicar- 
bonate) in sea water was always below the saturation point, and 
therefore direct precipitation due to concentration could not take 
place, yet sodium carbonate or ammonium carbonate might arise, 
due to the decay of plant or animal tissues, and that these reagents 
would precipitate the calcium carbonate from the ordinary sea 
water, under either cold or warm climates, in the form of aragonite, 
and that in this way the odlite grains were formed. 
This theory does not eliminate the organic factor in the pro- 
duction of odlite grains, but makes the organisms indirect agents 
which produce by their decay sodium or ammonium carbonate, 
the precipitating reagents, instead of directly building the odlite 
grains by their organic activity. 
It would therefore seem that under either the organic or inor- 
ganic theory of origin we must postulate the presence of organisms 
t Neues Jahrbuch fiir Min., Geol., und Pal., Beilage-Band XVI (1903), 495-513. 
