File:The Quarterly journal of the Geological Society of London (13206023454).jpg

ROBERTSON ON THE WEALDEN BEDS OF BRORA. 113
posterior portion of eacii volution between the ends of the ribs and
the suture. Aperture oblong-ovate, both lips smooth, canal modeft
rately long, and curved to the right. Length '55 inch, breadth
•15 inch, jHrst volution *25 inch : angle of spire 30°.
Mitra juniperus, Strickland. — Taper, with ten or
eleven slightly rounded volutions. On each volution
are from twenty to twenty-two slender, rounded, tole-
rably regular, longitudinal ribs, becoming evanescent
towards the suture, which is distinctly marked by a
fine line. The intervals between the ribs are in
general slightly wider than the ribs themselves, and
are shallow, flattish, and furnished with fine irregular
longitudinal wrinkles, especially on the first volution.
Both ribs and intervals are crossed by nine or ten fine
thread-like striae, producing a reticulated surface ; two Mitra juniperus.
of these are at the posterior part of the volution near
the suture ; in front of these is a smooth zone, equal to about one-
fifth of the exposed part of the volution, which is destitute of striae ;
the remaining striae are at the anterior portion of the volution. The
anterior portion of the first volution has in addition about twenty
more striations, regular and closely compacted, which are concealed
by the succeeding volution. Aperture narrow ; columella with three
strong, rounded spiral folds, the hindermost largest, the anterior one
slight, their intervals broad, flat and smooth ; between the two ante-
rior ones is a slight trace of another. The medial portion of the
outer lip is occupied interiorly by eleven or twelve raised thread-
like lines, which penetrate into the mouth as far as can be seen.
Length about 1*6 inch, breadth '45 inch, first volution '6 inch :
angle of spire 1 8°.
On the Wealden Beds of Brora, Sutherlandshire, with Re-
marks on the Relations of the Wealden Strata and Stonesjield
Slate to the rest of the Jurassic System, and on the marine con-
temporary of the Wealden Series above the Portland Stone. By
Alexander Robertson, Esq., F.G.S.
.Read May 20, 1846..
In the spring of 1843 I had the honour of transmitting to the
Society a short account of two beds containing freshwater fossils,
which were found by me, during the preceding summer, intercalated
with the carboniferous portion of the Jurassic series of Brora*.
Having been prevented at the time of the discovery from making so
detailed an examination of their relation to the rocks with which
they were associated as was desirable, I again visited the locality, and
now present the result of my observations on that occasion.
My first object was to determine the exact age of the marine
bed immediately above the main seam of coal, and with this view I

• Proc. Geol. Soc. vol. iv. p. 173.