238  Correspondence—Dr. C. Callaway—Prof. Prestwich. 
course indebted to Messrs. Wright and Buckman for their researches, 
and if necessary the names of species taken to characterise given 
zones must be altered in accordance with their determinations. In 
no department has our nomenclature yet reached perfection, and as 
Mr. Buckman says, we must effect changes of name as our know- 
ledge increases, but at the same time we must agree upon general 
systematic principles. A. J. Juxes-Browne. 
SHIRLEY, SOUTHAMPTON. 
GLAUCOPHANE IN ANGLESEY. 
Sir, —The interesting paper by Prof. Blake, ‘‘On the Occurrence 
of a Glaucophane-bearing Rock in Anglesey,” which appears in 
your March issue, suggests a question of nomenclature which is 
likely to give us some trouble. Jam very glad to have Prof. Blake’s 
support in assigning ah igneous origin to some of the Anglesey 
schists ; but now that they are schists I should hesitate to call them 
‘joneous.” In Prof. Bonney’s description (quoted by Prof. Blake) 
of a specimen from the Anglesey column, the constituent minerals 
are “probably a species of chlorite,’ ‘epidote,” “ quartz (?),” and 
“mica”; and they form ‘a foliated dense felted mass.” According 
to my view, in which I understand Prof. Blake to acquiesce, this 
rock was once a diorite (hornblende and plagioclase). If so, the 
change from the eruptive ‘rock to the schist is surely entitled to be 
called a metamorphosis. If we apply the term ‘ igneous” to a 
crystalline schist when we can assign to it an eruptive origin, must 
we call it “aqueous” when we know it was once a sediment? And 
under what head must we class it when its genesis is unknown to 
us? I grant that in tracing a diorite or a granite into a schist, we 
cannot fix a hard boundary-line between the two; but a similar 
difficulty meets us in the study of metamorphosed sediments, and it 
is not found to be very serious. However, I write rather to raise 
a question than to settle it. If we are not to call crystalline schists 
by the term “ metamorphic,” how shall we designate them? They 
would be as sweet to me by any other name. 
WELLINGTON, SALOP. Cu. CALLAWAY. 
THE ATMOSPHERE OF THE COAL-PERIOD. 
Str,—In the review of the 2nd Vol. of my treatise on Geology 
which appeared in the last number of your MaGazine, your reviewer 
remarks (p. 161), “The author considers that, during the Coal-period, 
the atmosphere was more dense, and more charged with moisture and 
carbonic acid, and he is led ‘to conclude that the coal-growth was 
in all probability one of extreme rapidity, and consisted of woods and 
plants containing a much larger proportion of carbon than any existing 
forest vegetation.’ With regard to the excess of carbonic acid gas, 
Mr. Carruthers has expressed an adverse opinion, and experiments 
made on living plants have shown that they are liable to be poisoned, 
like animals, by an excess of the gas.” <A footnote to this passage 
refers to Grou. Mac, 1869, p. 300, and 1871, p. 497. The first is a 
