Maryland Geological Survey 17!) 



solved only by getting different stages in the processes involved, and 

 perhaps by chemical analysis, and the present observations are not con- 

 sidered as sufficiently extended to give ground for interpretation of the 

 facts observed. 



In view of the very undeveloped state of knowledge of the actions of 

 colloids, the uncertainty about the processes involved in the formation 

 of glauconite is very comprehensible. The known power of colloids to 

 absorb without chemical combination variable amounts of different sub- 

 stances may also account for the indefinite composition indicated by 

 analysis. Against this apparent variability Collet's protest ' that most 

 of the samples analyzed were not made up of perfect glauconite seems 

 invalid since his only criterion was fresh green color and, and there is 

 no evidence that within material of this green color there are not imper- 

 ceptible variations in degree of what he himself (p. 176) calls " glauconiti- 

 zation." Indeed, the wide difference in tone between samples of glauco- 

 nite from different localities would seem to indicate that there is such a 

 variation. The only analysis that could by itself definitely be set up as 

 establishing the composition of glauconite would be of good crystals of the 

 substance, but recognizable crystals identified as glauconite are so rare and 

 so small when they do occur that chemical analysis has not been possible/' 

 Moreover, it may well be that glauconitization does not tend at all toward 

 the formation of a single definite compound and that different glauconites 

 are only different members of a series like the chlorites to which they arc 

 by some supposed to belong, or like other micas. That this is probable is 

 indicated by Collet's discussion* of the crystal identified by Cayeux, 

 which lie shows has different optical properties from others that have 

 been described. 



However, there is strong evidence in favor of Collet's view of the 

 process. First of all, it seems certain that it must start from clay, since 

 the foraminiferal shells are sure to be filled with that substance by the 

 progress of sedimentation. Murray's assumption of sulphuric acid to 



1 Collet, L. W., Op. cit, p. 167. 



2 See discussion of determined crystals in Collet. 



3 Collet, L. W., Op. cit., p. 136. 



