148 The Petrography and Genesis of Sediments 



(e) Magnetite 

 Very angular, with a few rounded grains. Much glauconite included. Some garnet. 



//. Extra Fine Sand 

 Largely glauconite in irregular grains. 



///. Silt 

 Nothing of interest. Mineral grains, much mica, glauconite. Very few limonite flakes. 



Summary and Conclusions. — This sample, which may be considered 

 typical of the fades of the Matawan in this neighborhood, is interesting, 

 first of all for its marly character, that is for the combination in it of clay 

 and high lime content with glauconite. With the high lime content goes 

 a great richness in fossils. I can see no reason for considering this differ- 

 ence other than primary, since there is no factor apparent that would pre- 

 serve the lime here more than in other occurrences. Of course it is 

 assumed that foraminifera originally occurred in all the primary glau- 

 conitic rocks, but their shells would form merely a thin coating on the 

 individual glauconitic grains, not a calcareous argillaceous mass through 

 which the glauconite might be distributed. It is, therefore, fair to assume 

 that the bed was formed under conditions unusually favorable to the life 

 of neritic shell bearing forms. 



The diagram for the sample (K, p. 169) is that of a rather normal open- 

 water off-shore sediment, with sorting, however, less perfect than in 

 marine off-shore deposits. 



In the mineral composition there is noteworthy the occurrence of sev- 

 eral minerals scarce or very rare in other samples, especially hornblende, 

 augite, apatite, and andalusite. The unusually good preservation of the 

 crystal form of rutile indicates its derivation from nearby. 



The general fresh condition of the glauconite is characteristic for the 

 sample. In view of this fact it does not seem probable that the irregular 

 grains of glauconite with inclusions represent a decomposition product, 

 for in that case some intermediate stages would be expected. More prob- 

 ably, therefore, they are a distinct type of glauconitic product. Their 

 form and ocurrence suggest analogies with the limonitic flakes in many 

 samples, which are probably mainly small encrustations loosened from 

 the grains on which they occur. In the same way these would be loosened 

 flakes of glauconite encrustations, such as are found on the surface and in 



