Griswold.] 418 [Dee. 19, 
which would outweigh the argument from lithological association. 
For this reason it is necessary to considei- in detail the more 
important arguments offered by Mr. Rutley. 
Consideration of Mr. Rutle)/s theory. — From a study of 
specimens of the two rocks of the novaculite series which are 
used as whetstones, and from a study of the data presented in 
the " Report," Mr. Kutley is led to advocate that the novaculites 
are " siliceous replacements of dolomite or of dolomitic iimestone- 
beds."i There are two main lines of argument ; that the ground- 
mass of silica is chalcedony instead of quartz, and that the 
rhombohedral cavities indicate a previous greater quantity of a 
dolomitic carbonate. The observations supporting the first 
argument are two : first, that Arkansas stone under the 
microscope looks like flint, and "•the structure of Ouachita stone 
is similar but coarser in texture" ; secondly, the specific gravity 
of novaculite favors the idea of a groundmass of chalcedony 
rather than of quartz. To support the second argument reason 
is given for believing that the original carbonate was a dolomite, 
and second, the outlines of the cavities are such as to induce 
))eUef that the carbonate of these cavities represented a mere 
residue of a greater mass, the replacement by silica being shown 
by the relation of the grains of silica bordering the cavities to 
the dolomite formerh' occupying them. 
\ discussion of the resemblance of novaculite to flint requires 
first an understanding of the terra flint. Now the writer felt 
great difficulty on entering the subject of the fine-grained sili- 
ceous rocks on account of the varied use of different terms by 
many writers. Therefore the writer selected for his own use 
definitions which seemed best established in literatui-e.-' Mr. 
Hiitley seems to accept the writer's definition of chert, but appar- 
ently favors the idea that the siUca of flint may be chalcedonic. 
Bv the writer flint was regarded as a siUceous rock containing a 
considerable proportion of opal silica ; as such a definitiori has 
good authority and gives a means of distinction from chert the 
writer adheres to it. Xovaculite is without opal silica ; the dis- 
tinction between novaculite and flint was regarded as clear, and 
as nobody had advocated an origin of novaculite from flint there 
• Opus vit., p. 38G. 
■i Opus fit., p, 178-18T. 
