510 /. K. PRAT HER 



rounded, but, except for one instance, there seems to be no indication 

 that a shell once surrounded them. In one sample the perfect shells 

 of Foraminifera were found among the glauconite grains, which 

 would seem to oppose the idea that the glauconite was first contained 

 in the shells, which were afterward dissolved by the action of sea 

 water. 



While glauconite does not have the concentric lines generally seen 

 in the oolites, yet the similarity in shape and structure to grains of 

 oolite, which do not show the concentric lines, suggests that many 

 of the rounded grains of glauconite are concretions, and formed in a 

 manner similar to that of the oolites. In some grains of glauconite 

 was noted an indication toward concentric lines. The silica, lime, 

 and iron which form the oolites tend to take the concentric structure 

 more readily than does the glauconite. 



The New Jersey beds contain glauconite in pockets, masses of 

 glauconite, grains with some cementing clay, or as disseminated 

 grains of glauconite. Where there is much clay present, the condi- 

 tions are not so favorable for the further concentration of the glau- 

 conite as when it is more arenaceous. 



The Navesink, a greensand bed from which most of my samples 

 were taken, is composed of grains of glauconite with more or less 

 clay and fragments of the older rocks. It also contains a clay iron 

 stone, concretionary in form, which contains grains of glauconite. 



The Redbank sand overlying the Navesink is composed of quartz 

 grains, and contains glauconite which is easily affected by water and 

 oxidizes, and gives the red and yellow colors so prominent in this bed. 

 I have picked out round grains of magnetite with a weak bar magnet 

 from this material which may have been originally grains of glauconite. 

 Limonite is seen filling cracks in the clay bed at the top of the Nave- 

 sink underneath and replacing fossils. 



Pieces of limonite the size of a hand were collected from the 

 Redbank. The slides in which the grains show the greatest altera- 

 tion are from samples from the Redbank. 



Van Hise 1 shows that hematite, limonite, magnetite, greenerite, 

 pyrite, etc., change from one form to the other, so that glauconite 

 altering to one form may be changed into any of the others. 



1 Monograph 47 of the U. S. Geological Survey, on "Metamorphism." 



