188  Correspondence—Ur. J. 8. Gardner—Dr. C. Callaway. 
growth or accretion is such as occurs in Annulose and not in Mollus- 
cous shells. One of the specimens contains a Ditrupa and a Spirorbis 
both of which exhibit precisely the same kind of microscopic structure.””* 
While some of the supposed patelliform shells cannot be placed 
among the Mollusca, one form, of which there are two specimens, is 
very well preserved and distinct. It is referred by Gwyn Jeffreys to 
the genus Hipponyx, of which no upper valves were known previously 
from any strata below the Maestricht Limestone, although the lower 
valves or shelly bases had been met with in both the Chalk and Green- 
sand in England. 
_ ‘They are from the Glauconitic Marls of the Black Mountain, Belfast, 
from the zone of Pecten asper of Barrois. 
I have also received within the past week a new Zmarginula from 
the Grey Chalk near Folkestone, which differs markedly from the only 
form hitherto known, Z. Gresslyi, from that locality. I hope to illus- ~ 
trate both these in a future number of the GrotocicaL MAGAZINE. 
J. STARKIE GARDNER. 
COMPARATIVE PHYTOLOGY, 4, 
_ Sra,—Some very indistinct impressions, or rather remains of leaves, 
were forwarded to me from the well-known hazel-nut bed of Brook in 
the Isle of Wight, under the supposition that they might prove to be 
leaves of the beech. It is interesting to record that Baron von Ettings- 
hausen found himself able to at once pronounce them to be leaves of 
Corylus, although he was quite unaware that they had been found 
associated with the nuts, and therefore recognized them entirely from. 
what could be traced of their venation, for the outline and margin 
were almost wholly obliterated. J. STARKIE GARDNER. 
THE TERM “SCHIST,” 
Str,—I feel rather perplexed by some observations on the term 
‘schist’? made by Mr. Allport in the Grox. Mae. for this month. A 
great deal of confusion at present prevails as to the exact meaning of 
the word, and the progress of our knowledge, as I know by experience, 
is impeded by the want of a fixed meaning. Following Jukes, I have 
usually confined the terms ‘‘schist”’ and ‘‘schistose’’ to a rock pos- 
sessing true foliation, as defined by Darwin, and approved by Mr. 
Allport. But when I have come to study certain ‘schists’ in the 
field, I have found them to be simply laminated or cleaved, and there- 
fore not schists, but shales or slates. It has appeared to me that we 
could not do better than adhere to Jukes’s summary of the different 
kinds of fissile structure: ‘the foliation of schist, the cleavage of slate, 
and the lamination of shale.” I was accordingly cast in doubt on 
finding that so high an authority as Mr. Allport used ‘‘schistose” as 
equivalent to ‘‘fissile,” and affirmed that ‘‘the term schist certainly 
ought not to imply or include foliation.”” I confess I do not see why 
the word “fissile” could not be used for rocks which do not come into 
Jukes’s triad, leaving as ‘schistose”” undecomposed and unmetamor- 
See Dr, Gwyn Jefireys’s report of the Valorous Expedition, Proc, R.S. 1876. 
