VOLCANICS OF THE MICHIGAMME DISTRICT. 821 
for its post-Tertiary .equivalent,—in spite, too, of the fact that 
the great resemblance between such rocks has been frequently 
emphasized. 
In a paper published in 1893, upon the acid rocks of the 
region described in the preliminary paper by Williams,* Miss 
Bascom? proposes ‘‘to call the acid volcanic rocks whose struc- 
tures prove them to have once been glassy, apforhyolites, while 
those which have consolidated at a sufficient depth to secure a 
holocrystalline groundmass should be termed quartz-porphynes, 
whether ancient or modern lavas,” the moment which is to deter- 
mine the use of the name being the “specific alteration known 
as devitrification.”’ Thus, using the term rhyolite in its present 
sense, extended however so as to include its pre-Tertiary equiv- 
alents, we may have rhyolites of all ages, and likewise aporhyo- 
lites of all ages. It was proposed also to apply the prefix ao 
to all other devitrified rocks. 
Independently of Miss Bascom, and shortly after her paper 
appeared, Nordenskjéld proposed, before the Students’ Associa- 
tion of Natural Science of the University of Upsala,3 the names 
eorhyolite, eobasalt, etc., for the old equivalents of the rocks known 
as rhyolites, basalts, etc. It appears to me preferable to use the 
nomenclature proposed by Miss Bascom, both on the grounds of 
priority and of expressiveness, as the name indicates in what con- 
dition we will find the rocks, whereas the names proposed by 
Nordenskjéld would merely mean an addition to petrographical 
literature of new names to express conditions which are already 
expressed by names at present in use. Thus under eorhyolites 
we have rocks placed in opposition to the neorhyolites, which as 
a result of their age are probably very much altered, though this 
condition is not necessary for the correct application of the term 
as I understand it. It is possible that at some time there may 
be found an insignificantly altered rock which must be classed 
with the eorhyolites. On the other hand, we will undoubtedly 
“ILO Cit, 
2 The Structures, Origin, and Nomenclature of the Acid Volcanic Rocks of South 
Mountain. Jour. oF GEOL., Vol. I., No. 8, p. 829. Nov.—Dec., 1893. 
3 Loc. cit., p. 292, meeting on November 18, 1893. 
