134 The Petrography and Genesis of Sediments 



(d) Xon-magnetic. 



Zircon and enstatite, about equally abundant. Kyanite very rare. 



(e) Attracted by permanent magnet: Mainly magnetite but. witb much chlorite, some 

 biotite, and a little glauconite. Magnetite in very angular grains. 



II. Ejrtra Fine Sand 

 Mainly quartz with some glauconite and mica. 



III. Silt 



Dark gray with a yellowish tint. Many limonite flakes. Much mica. A fibrous 

 serpentinous mineral common. 



IV. Clay 



Yellowish showing much limonitic matter. Much fibrous matter. 



Summary and Conclusions. — The most striking feature of this bed is 

 the evidence of reworking of the material in it. Thus, except in the 

 coarsest sand, there is almost no glauconite in primary botryoidal form, 

 the grains being mostly rounded. 



I think the ocherous stain of the grains throughout, the sand-ocher 

 concretions, and the weathered condition of the feldspars may be inter- 

 preted in the same way, for it does not seem as though such products 

 could be formed in a sediment as argillaceous as this while, moreover, the 

 bed itself remained black and free from ocherous stain. It seems more 

 probable that they originated in a more open-textured glauconitic sand 

 exposed to atmospheric agents before its constituents were reworked and 

 redeposited in this bed. 



The other principal feature is the evidence that seems to me to point 

 to something like a delta facies for this bed. The factors indicating 

 this are : 



1. The mechanical composition of the sediment as shown in C, p. 169 

 (cf. D and J, p. 170). The material is seen to be unsorted, all sizes being 

 well represented, though the three finest largely predominate. This poor 

 sorting suggests a small body of water, either a lagoon or a quiet open 

 stretch of water in a delta, while the sharp rise of the curve from the fine 

 to the very fine sand with a slow drop to the right has been shown in the 

 general discussion of these diagrams to be characteristic of stream sedi- 

 ments. 



2. The abundance of mica. 



3. Abundance of carbonaceous matter. 



