1894.] 4:15 [Griswold. 
uplift extend three or four hundred miles farther west, but for 
how much of this distance the novaculites persist is not known. 
The strong ridgemakers of the belt are three : some massive 
quartzose sandstones of the Lower Carboniferous formation ; some 
pure siliceous rocks of very much tinei- grain in massive beds 
aggregating 500-600 feet, belonging in the upper part of the 
Lower Silurian and known as novaculites; and below the nova- 
culites another series of massive sandstones. The i-ocks of the 
valleys are chiefly shales which give gradations from well-detined 
argillaceous, ferruginous, and carbonaceous varieties, througli 
more siliceous kinds to very pure siliceous layers. Limestones 
also occur, dark blue in color, and believed to be generally 
magnesian though not widely tested. 
Restatement of the argument of origin. — It is maintained 
tliat the novacuUtes of Arkansas are simple, fine-grained, siliceous 
sediments derived mechanically. Thus they are sandstones of 
extremely fine grain ; sandstones rather than quartzites because 
there is reason to believe that secondary silica cementing the 
grains is small in quantity. The reason is based first upon the 
qualities which novaeulite has as a whetstone — qualities whictli 
necessaril}' allow particles of whetstone to be rubbed away in 
order that fresh scratching points may be presented to the tool 
— and quartzites are too firmly cemented to admit of use as 
whetstones; and secondly, a thin section of quartzite under the 
microscope shows the sides of the grains in extremely close 
contact without interspaces, while in novaeulite the individual 
})articles seem less closely united. 
The rock is evidently of sedimentary origin since it occurs as a 
definite member of a sedimentary series which is of continuous 
and wide extent, and since a microscopic examination shows 
quartz grains well rounded by mechanical action, of larger size 
than those of the groundmass of the stone. For these coarser 
grains the mechanical origin is evident, but one might urge that 
the fine particles of the groundmass were a direct chemical 
precipitate from sea water, as there is no essential difference 
between these particles, and those of silica powder produced in 
the laboratory. Direct chemical precipitation would be a matter 
of pure hypothesis, whereas the greater part of the fine siliceous 
incfredient of slates and shales which is also identical with the 
