A CONTRIBUTION TO THE OOLITE PROBLEM 797 



sinuous fibers. In some instances, however, the two outer bands 

 grade gradually into each other without any distinct line of demarka- 

 tion; or indeed the radial structure may be entirely wanting and the 

 concentric structure may continue into the nucleus. The fibers are 

 best shown in peripheral sections of the grains. In these they 

 appear to enwrap the bodies. 



Some of the grains, however, show little or no trace of algal 

 fibers, but there is convincing evidence that this fact has resulted in 

 most, if not all cases, from the obliteration of original structures as 

 an accompaniment of silicification. All stages of such obliteration 

 may be traced under the microscope. 



