F 
oo ihe 
TRANSACTIONS OF SECTION C. 807 
and increase the likeness to true volcanic vents are later than the period of 
crushing, and may be traced in the surrounding slates and grits. 
But though the volcanic nature of the rocks formerly believed to be agglome- 
rates must be abandoned, the question of the original formation of the strata which 
have been so greatly ruptured remains quite distinct. The author agrees with 
Mr. Blake in regarding these strata as largely composed of volcanic detritus. The 
breccias and fine tuffs which alternate with and overlie the Lower Silurian black 
shales can be traced upward into the mass of the Amlwch slates, which are full of 
volcanic dust. The evidence for the existence of Lower Silurian volcanoes in the 
north of Anglesey remains quite valid and ample, though we must abandon the 
voleanic origin of the ‘agglomerates’ which seemed to form part of that evidence. 
The crush-conglomerates have involved the volcanic as well as the non-volcanic 
paris of the series in the same destruction. But it is obvious that in a region 
which has undergone such severe compression and disruption it cannot be always 
an easy task to distinguish between breccias due to original volcanic explosions 
and those produced among these yery volcanic rocks by subsequent mechanical 
stresses. 
9. Report on Seismological Investigations.—See Reports, p. 180. 
10. Note on some Fossil Plants from South Africa. 
By A. C. Sewarp, JLA., FGA. 
The author has recently had an opportunity, through the kindness of Mr. Dayid 
Draper, F.G.S., of examining a collection of fossil plants from a locality a short 
distance south of Johannesburg. The collection forwarded to England by Mr. 
Draper includes examples of Glossopteris,, Vertebraria, and other genera, asso- 
ciated with specimens of Lepidophloios The occurrence of Lepidodendrons 
in strata containing typical members of the Glossopteris flora is extremely 
important from the point of view of the geological and geographical distribution of 
fossil plants, and specially interesting in connection with a similar association lately 
recorded by Professor Zeiller in Brazilian plant-bearing beds. In South Africa, as 
in South America, we have evidence of the existence of a plant genus characteristic 
of the Upper Paleozoic flora of the northern hemisphere, in the same region with 
the Permo-Carboniferous Glossopteris flora. 
11. On the Production of Corundum by Contact Metamorphism on 
Dartmoor. Ly Professor Karu Busz. 
At South Brent the valley of the Avon cuts right through the contact-zone of 
the Dartmoor granite. The clay-slate is altered into chiastolite slate and spotted 
_ mica schist, and small interbedded seams of limestone are represented by aggregates 
of garnet, malacolite, axinite, and what seems to be anorthite. The crystals of 
andalusite in one of the altered slates have proved to contain a small quantity of 
cassitorite in minute crystals. This stream also exposes the intimate contact 
between a felspar porphyry and clay-slate: irregular pieces of the latter rock are 
included in the former. Around these pieces there occurred a large number of 
minute colourless hexagonal crystals, which, when isolated by the action of hydro- 
fluoric and hydrochloric acids, proved to consist of alumina with a very little iron 
oxide, Their hardness was also greater than that of topaz, so that it is clear they 
must consist of corundum. In the opinion of the author the melted porphyry has 
dissolved the clay, and thus become supersaturated with alumina, which has 
erystallised out as crystalline corundrum. 
12. Interim Report on the Age and Relation of Rocks near Moreseat, 
Aberdeen. 
