On the Geology of the Troad. 157 
teristic of the estuaries of the Severn and its tributaries, such as the 
rivers themselves, the waste of mud shoals, or of bordering cliffs, 
or the sea. The author considered the effect of these sources of 
supply, and showed that, although the first three are doubtless to a 
certain extent correct, they are inadequate to account for some 
very important phenomena. The tidal silt, on microscopic exami- 
nation, is found to consist of both inorganic and organic materials, 
the former being argillaceous granules, grains of quartz, flint, &c. ; 
the latter, coccoliths, coccospheres, Eoraminifera, occasional sclerites 
of Alcyonaria, fragments of Echinodermata, and triradiate spicules of 
Calcispongia, together with numerous spicules of siliceous sponges, 
a few Radiolaria, and a variable quantity of Diatoms. These 
organisms (described in detail by the author) are marine, and yet 
they occur on the banks of rivers at a great distance from a truly 
marine area. The author showed it to be improbable that they can 
have been derived, at any rate to a considerable extent, either from 
the older formations through which the Severn flows, or from the 
alluvial flats of its estuary ; for although the latter do contain 
marine organisms of a generally like kind, the spicules &c. indicate 
corrosion, and are generally not so well preserved as those which 
occur in the tidal silt. It seems therefore necessary to conclude 
that a considerable proportion of the organisms now present in this 
have been brought from the sea ; but sponges are not known to 
grow in any quantity nearer Bristol than the coasts of Devon and 
Pembrokeshire. It would therefore appear that these organisms, 
contrary to what might have been expected, have been drifted up 
into the tidal estuaries of the river for a very considerable distance. 
The author concluded by describing in detail the alluvial tracts of 
the Severn, which he considers to have been formed (with certain 
differences of level) much as tidal deposits are formed at the present 
day ; and by pointing out the bearing of his investigations on the 
question of the probable results of the discharge of sewage into 
tidal rivers. 
2. " Notes on a Collection of Fossils and Rock-specimens from 
"West Australia, north of the Grascoyne River." By W. H. Hud- 
leston, Esq., M.A., E.G-.S. 
3. " Notes on the Geology of the Troad." By J. S. Diller, Esq. 
Communicated by W. Topley, Esq., E.G.S. 
This paper gave a brief account of the results obtained by the author 
whilst attached to the United-States Assos Expedition. Together 
with a geological map (scale 1 : 100,000), this was sent to Mr. Topley 
for the service of the new Geological Map of Europe (and its borders), 
which is now being prepared by a Committee of the International 
Geological Congress. 
The country described is that lying south and west of the river 
Mendere (Scamander). The sedimentary rocks may be divided into 
three great groups : — 
(1) An old, possibly Archaean, highly crystalline series, forming 
the mountainous lands of the Ida range (5750 feet), but also 
Phil. Mag. S. 5. Vol. 16. No. 98. August 1883. N 
