156 The Petrography and Genesis of Sediments 



have been studied and the material in them not found so weathered it is 

 justifiable to conclude that the sands of this sample were weathered 

 before they entered the bed. This would presumably be the interval cor- 

 responding to a disconformity between the Magothy and Matawan during 

 which sedimentary beds from which this material was derived were 

 exposed to atmospheric weathering. The absence of glauconite also tends 

 to confirm this belief, for while the beds contributing it to the Magothy 

 (in which it is all reworked) might have just become exhausted with the 

 closing of the Magothy, it is very improbable that the two phenomena 

 would so closely agree in time, and much more probable that there had 

 been a considerable interval during which either the glauconitic beds were 

 completely eroded, or the glauconite entirely decomposed. 



SAMPLE NO. 10 (FIG. J, p. 169) 



Serial number : 4. 



Field number : 4-9-28-1911. 



Formation : Matawan just below the contact with the Monmouth, or basal Monmouth. 



Locality : Sassafras River. 



Appearance : A greenish-yellow, lumpy, crumbly sand, full of limonite spots and with 

 some tinges of a lavender-brown clay. Under the hand lens it shows rather angular 

 quartz sand with small, rusty grains of glauconite; and throughout the mass, but 

 seemingly related to the glauconite, an cpidote-colored stain. On a freshly-broken 

 surface the lavender-brown argillaceous matter is evident. 



Mechanical Analysis 

 Sample for gravel 1 205.075 gm. 



Per cent of 

 sample 



Medium gravel 0.4 



Fine gravel 1.6 



Sands 98.0 



Total 100.0 1 



Sample for sands and clay 10.236 gm. 



Per cent of 

 sample 



Sands 2 62.1 



Silt 3.7 



Clay 24.1 



Total 89.9 



Per cent of 

 total sands 



Coarse sand 1.1 



Medium sand 37.6 



Fine sand 43.6 



Very fine sand 14.2 



Extra fine sand 3.5 



Total 100.0 2 



1 By summation of parts. 



2 Total sands by summation of parts. 



