Naming Rocks. 159 
the original planes of deposit, but are the result of 
cleavage. Color, gray, blue, green, purple, and somtimes 
black. Roofing slate is a compact kind which splits into 
very fine and even sheets. 
Argillyte—A slate in which more or less mica is 
present. The flakes of the mica occur in layers along 
the cleavage planes, a result of metamorphism. 
Sandstone—Consolidated sand. It bears the same 
relation to sand as conglomerate does to gravel, and is 
the result of cementing action. Sandstones are com- 
posed principally or wholly of the mineral quartz. ‘They 
are of various colors. Calcareous sandstone is a variety 
containing lime of a gray to white color. 
Conglomerate—Is gravel consolidated into a com- 
pact mass, made up in part of rounded pebbles cemented 
together. 
Grit—A variety of sandstone more common in the 
older than in the later formations. It is composed of 
coarse, angular grains of quartz, which point to its ar- 
rangement in strata and consolidation in stone with- 
in a short space of time after its separation from its 
parent rock. | 
Quartzyte—A compact, exceedingly hard rock, com- 
posed of granular quartz. It is a metamorphic sand- 
stone, and it occurs in interstratified beds. 
Flagstone—A sandy-slate, or a slaty-sandstone. 
Loess—A sandy, light-colored clay. It is dry and 
compact. — 
Till—A glacial-age deposit of boulders, clay, etc. 
Fuller’s-earth—A fine-grained argillaceous powder, 
when pulverized. 
