1894.1 417 rCriswold. 
the rock is the strongest argument against metamorphism. A 
columnar section^ of the rocks including the novaculites comprises 
sandstones, limestones, shales, and siHceous shales grading into 
true novaculites. Beds of all the above rocks at one place or 
another lie adjacent to siliceous beds sufficiently pure and fine- 
grained to be called novaculites. The sandstones have been 
somewhat cemented by secondary silica, but would scarcely be 
regarded as quartzites. Two localities of limestone are recalled 
where the rock contained \'isible crystals of the calcareous mate- 
rial indicating secondary action, elsewhere the rock texture was 
too fine for determination by the eye. Veins of calcite occurred 
very commonly along joint planes. The more clayey shales 
received no investigation which would throw Ught on the matter 
of metamorphism ; the more argillaceous layers of the siliceous 
shales'- examined microscopically showed miniite flakes of sec- 
ondary muscovite. The rocks intimately associated with the 
novacuUtes thus evidence a mere beginning of metamorphism, so 
that it does not seem reasonable to suppose either that the above 
novaculites have been derived from any one of the other kinds 
of rock by metam()r))hism or that in itself it lias undergone much 
change. 
A petrographic study of the novaculite disclosed evidence of 
just about as much secondary change in the rock as one might 
expect. Ill all samples were evidences of a disseminated Ume 
carbonate either by rhombs of the carbonate itself, apparently 
calcite, in specimens from valley bottoms, or by rhombic cavities 
in the stone from the mountain sides, produced by the solution 
and removal of the carbonate. A few of the smaller rhombic 
cavities have been filled by secondary silica ; small quartz veins 
occur ; and in those specimens containing more impurities occa- 
sional small spherulites of chalcedonic silica were noted. Thus 
the direct evidence indicates a condition comparable to that of 
the other members of the series. 
It may be m-ged that the above observations on petrography 
are prejudiced, that a minimum of alteration has been accepted 
while there was a possible maximum, and that another observer 
might elucidate evidences from a study of the rock in question 
1 Ann. rept. geol. surv. Ark. for 1890. v. 3. \>. 209. 
* Opus cU., p. 239, slides 41, 42, 43. 
PROCEEDIXGS B. S. X. H. VOL. XXVI. 27 JAX. 1896. 
