152 The Petrography and Genesis of Sediments 



difference is a secondary one that might be expected from the loose texture 

 of the upper bed as against the compactness of the lower — namely, more 

 limonitic matter in the upper. But it is very interesting to note that the 

 glauconitic staining of mineral grains is not one of these secondary dif- 

 ferences ; nor the apparently altered opaque condition of the glauconite ; 

 which would thus seem to have been produced before the beds were 

 emerged. 



The two beds are thus so intimately related that if it were not for the 

 accumulation of oysters in the top of the lower bed one would be led to 

 assume continuous deposition. The essential difference is in the presence 

 of abundant shells in the lower bed. It may be that the somewhat less 

 agitated condition of the water in which the upper bed was deposited 

 produced enough difference to make the area relatively unfavorable for 

 the animal life which had abounded at the time the lower bed was formed. 

 In any case the change appears to have been a subtle one. 



SAMPLE NO. 9 (FIG. I, p. 169) 

 Serial number : 19. 

 Field number : 17-9-28-1911. 

 Formation : Matawan. 



Locality : Grove Point, mouth of Sassafras River. 



Appearance : Dark blackish-gray, fine-grained, micaceous, argillaceous sand with some 

 scattered pebbles of fine-grained white quartz too scarce to have been caught in 

 analysis. 



Mechanical Analysis 

 Sample 10.780 gm. 



Per cent of 

 sample 



Sands ■ 68.5 



Silt 2.1 



Clay 28.2 



Total 98.8 



Per ecnf'of 

 total sands 



Coarse sand 0.1 



Medium sand 0.4 



Fine sand 0.5 



Very fine sand 45.1 



Extra fine sand 53.0 



Total 99.1 



Per cent of 

 very fine sand 



Light 91.4 



Heavy 5.6 



Total 97.0 



