160 The Petrography and Genesis of Sediments 



(e) Three very dark grains apparently filled with black clay and green glauconite 

 stain. These are like the grains in sample 13 which are believed to be secondary quartz. 

 Under the microscope these grains show homogeneous polarization and much of the 

 included matter appears to be mica. 



II. Medium Sand 

 Mainly like the coarse with the following differences : 



(a) The smaller grains instead of being rounded, are sharp, fresh, angular, evidently 

 primarily so. Hounded grains are, however, still very abundant. 



(b) Dark minerals (mainly magnetite and mica) begin to appear. 



(c) There are more of the stained quartz grains. 



///. Fine Sand 

 Characterized : 



(a) By the appearance of rather abundant, rounded, yellow-green glauconite grains*. 



(b) By the angularity of the quartz. 



(c) By the freshness of the quartz, i. e., little stained sugary quartz and no secondary 

 grains with clay inclusions were observed. 



(d) By the abundance of carbonaceous fragments. 



(e) By the fact that there appears to be little, if any, increase in the proportion of 

 dark minerals, except glauconite. 



B. Under the Microscope 

 /. Very Fine Sand 



(1) Light 

 Greenish-gray with much mica. 



Quartz : feldspar = 95 : 5. 



No distinct secondary quartz or feldspar with black clay inclusions, though black clay 

 has penetrated into the fissures of a few grains, especially of feldspar. Glauconite 

 staining occurs but is not abundant. There is no limonitic staining. There are here, 

 as in sample 4, some of the rounded, clay-like grains showing a faint aggregate polariza- 

 tion, apparently transition forms to glauconite. Glauconite in rounded grains mostly 

 full of round black granules. 



(2) Heavy 

 The heavy minerals are : 



Glauconite, chlorite, muscovite, epidote, tourmaline, garnet, amphibole (colorless), 

 staurolite, zoisite, rutile, serpentine, enstatite. zircon, kyanite. 



The glauconite is full of black granules. The chlorite and muscovite are in the same 

 condition. 



//. Extra Fine Sand 



Dark-gray with many minute flakes of mica. 



There is a striking variation in the size of the materials. There are many small 

 opaque spherical grains, showing a broken yellow surface by reflected light, sometimes 

 agglomerated into small groups. They are doubtless pyrite or marcasite. 



///. Clay 

 Much short fibrous matter. Black spherules as in the extra fine-grained portion, prob- 

 ably iron sulphide. Flakes of mica. 



Summary and Conclusions. — The mechanical composition of this sample 

 calls for little special comment. Its diagram shows the moderate sorting 

 and the abrupt rise of the curve on the left with much slower drop to the 

 right, which has been shown to be characteristic of stream deposits in 



