214 BULLETIN OF THE NEW YORK STATE MUSEUM 



II. Fragmental Rocks 



Sandstones. 



Sandstones are made up of grains of sand which are 

 bound together by a cementing material, in a compact and 

 consolidated mass. 



The grains may be of varying sizes, from almost impalp- 

 able dust to small pebbles, and more or less rounded in 

 form. The cementing matter also may vary greatly in its 

 nature. From this variation, both in the grains and in the 

 cement, there is an almost endless gradation in the kinds of 

 sandstone. 



Quartz is the essential constituent, but with it there may 

 be feldspar, mica, calcite, pyrite, glauconite, clay or other 

 minerals, and rock fragments common to stone of sedi- 

 mentary origin. And these accessory materials often give 

 character to the mass, and make a basis for a division into 

 feldspathic, micaceous, calcareous sandstones, etc., accord- 

 ing as one or another of them predominates. 



The texture of the mass also is subject to a wide range of 

 variation, from fine-grained, almost aphanitic, to pebbly 

 sandstone, or conglomerate, or a brecciated stone in which 

 the component parts are more or less angular. 



Some of the brown sandstones of the Triassic age, quar- 

 ried near Haverstraw, are such conglomeratic and brecciated 

 sandstones. Accordingly as the grains are small or large 

 the stone is said to be fine-grained or coarse-grained. 



The variety in the nature of the cementing material also 

 affords a basis for classification. Siliceous sandstones have 

 the grains held together by silica. They consist almost 

 exclusively of quartz, and grade into quartzite. The ferru- 

 ginous varieties have for their cement an oxide of iron, often 

 coating the grains and making a considerable percentage of 

 the whole. The iron may be present as a ferrous oxide, or 

 in the higher state of oxidation as ferric oxide. Calcareous 



