136 The Petrography and Genesis of Sediments 



V. Extra Fine Sand 

 Dirty green micaceous sand. 



B. Undbe the Microscope 

 J. Very Fine Sand 



(1) Light 

 Quartz : feldspar=85 : 15 



General appearance silvery-gray, micaceous. 

 The quartz grains are of two kinds : 



(a) Glassy grains with more or less inclusions. 



(b) Rough, pitted, granular fragments with a greenish tinge. The green-stained 

 variety is, however, rare. 



Glauconite occurs in pale, olive-green, transparent, rounded grains, very fresh looking. 

 All kinds of feldspars except plagioclases were noted, in general appearing rather 

 rough and weathered but not kaolinized. 



(2) Heavy 

 (a) Magnetic 



General appearance light greenish-drab, with much muscovite and a striking absence 

 of glauconite and generally of dark minerals. 



Dominant. — Muscovite, chlorite, glauconite, serpentine. 



Subsidiary. — Garnet, tourmaline, biotite, calcite (?). 



The biotite appears much decomposed, some of it full of black grains (magnetite ?). 



(b) Non-magnetic 

 Dominant. — Zircon. 

 Bare. — Enstatite, garnet, calcite, kyanite. 



//. Extra Fine Sand 

 Appearance. Silver-gray with a greenish tinge. 



(1) Much glauconite in round grains, green, semi-transparent, fresh-looking. 



(2) Round, brownish grains specked with black. They look exactly like clay but 

 polarize faintly. They differ from the glauconite in that the glauconite is clear without 

 the black, granular inclusions. (Cf. Silt (III) below.) * 



III. Silt 



(1) Much argillaceous material in flakes or globules. 



(2) Rounded grains of transparent, granular, clay-like material of which the globular 

 form and aggregate polarization suggest that it may be incipient glauconite. 



(3) Pale, yellowish-green, transparent glauconite. 



(4) A few pale yellow, transparent, angular, granular, non-polarizing flakes, probably 

 of limonite. 



(5) Mineral grains are common. 



(6) There are large flakes of mica. 



(7) Black carbonaceous matter. 



IV. Clay 

 Appearance blue-gray. 



Pretty fine clay with much fibrous material which though dirty brown and clay-like in 

 appearance yet polarizes. 



The amorphous-looking clay also polarizes as an aggregate, probably on account of 

 minute included mineral fragments. Individual mineral grains are, however, unusually 

 scarce. 



Summary and Conclusions. — Two characters are particularly striking 

 in this sediment. 



(1) The foremost is the abundance of mica apparent in the original 

 specimen, but supplemented in the analysis by the high percentage of the 



1 Note that the clay was also found to have aggregate polarization though that may 

 have been due to included mineral fragments. 



