i894.] 419 l[GriswoId. 
was no further discussion. Tf Mr. Rutley now has a rock which 
is identical chemically and optically with novaculite and which 
he thinks should be called flint, then our discussion will be of a 
very different nature. Chert was the rock elaborately discussed 
in the " Report " because a theory of origin from chert had been 
advocated ; and furthermore, chert being by one of the writer's 
definitions " a crypto-crystalline siliceous rock formed by chemi- 
cal action, and containing a large percentage of silica in the 
chalcedonic form," was regarded as more nearly allied to 
novaculite than was flint, so that if rejected as a source of 
novaculite an origin from flint would be rejected by the same 
.arguments.! 
The wi-iter would not feel justified in making a general state- 
ment that the texture of Ouachita stone was coarser than Arkansas 
stone ; for there seems to be a very slight variation in size of 
grains in both stones, a fact perhaps explainable in part by dif- 
ferences in the thickness of the sections. 
The specific gravity of novaculite as determined by Griswold 
and Rutley respectively is i!.()48 and 2.6441, and these figures 
represent the specific gravity of the silica of the rock, as the 
groundmass is practically all one thing. Prof. ,J. J). Dana gives 
as the range of specific gravity for quartz "J. 058 to 2.(36 and for 
chalcedony 2.6 to 2.64 ; therefore Mr. Rutley concludes that the 
silica of the novaculites should be regarded as chalcedony rather 
than quartz. Disregarding the possibility that quartz may range 
lower than 2.658, let us consider what would be expected if the 
material is chalcedony. First, we should expect sometimes to 
find evidence of a fibrous structure, for it is improbable that many 
sections cut at random should fall squarely across the fibres of a 
chalcedonic mass. Fibrous spots in the novaculites are very 
small in size and few in number ; they are more abundant when 
impurities are present. Again, if the siUca is chalcedonic we 
should expect to get evidence from a test of solubility in caustic 
potash, for as far as the writer is aware chalcedonic silica gives a 
1 Mr. Rutley mentions cherts which give uo evidence of soluble silica in caustic 
potash, but a study of his references (Sci. trans, roy. Dublin soc, vol. 1, new ser. — 
On the nature and origin of the beds of chert in the upper carboniferous limestone 
of Ireland. By Prof. Edward Hull, M. A. F. R. S. ; and The chemical composition of 
chert and the chemistry of the process by which it is formed. By Edward T. Hard- 
man, F. C. S.) would indicate that probably no chalcedonic silica was present; conse- 
quently the writer cannot accord them weight in the argument. 
