94 Reports and Proccedings— Geological Society of London. 
accompanying the widespread province of Caledonian granites. The 
great bulk of “the deposits of economic importance, including the veins 
of Cornwall and Devon, the lead, zinc, and copper veins in England, 
Southern Scotland, Wales, and Treland, are of Hercynian (and 
Armorican) age. ‘This is shown by the age of the fissuring in many 
cases (post- Carboniferous to pre-Triassic), by the absence of ore-veing 
in Jurassic or later formations, and by other evidence. ‘The Tertiary 
voleanic period was not accompanied by ore-deposition, the evidence 
which has been adduced in favour of this in the Isle of Man, Cornwall, 
and Devon, and the North of England, being unsatisfactory. 
The ore-deposits are classified in accordance with the above- 
mentioned metallogenetic epochs, and are divided into metallogenetic 
provinces, as has been done by Professor L. de Launay with the ore- 
deposits of Italy, Africa, and Siberia. The essential features of the 
ditferent groups are summed up. The evidence, collected = sifted, 
indicates the following zones of ore-deposition :— 
(1) Pneumatolytic zone: tin, passing up into copper. 
(2) Deeper vein-zone: copper with gold. Lead and zine subordinate. 
(3) Middle and upper vem-zones : lead and zine. Copper subordinate. 
The conclusions drawn from the investigations are :— 
(i) The importance of the physical conditions of the Permo-Trias in 
favouring ore-deposition in upper zones. 
(ii) The close connexion between metallogenetic and petrographical 
provinces, and the essential dependence of ore-tormation throughout 
geological time on the differentiation of igneous rocks accompanying 
ereat crustal movements. Differences in ore-deposits in different 
localities and regions appear to be due to primary differentiation of 
ores accompanying the differentiation of igneous magmas at successive 
epochs. 
. “The Geological Structure of Southern Rhodesia.” By Frederic 
Philip Mennell, F.G.S. 
The author describes in some detail a portion of what may be 
termed ‘the Laurentian Area’ of Africa. The oldest rocks include 
all lithological varieties, and exhibit most of the known types of 
alteration. They comprise a great development of hornblendic rocks 
(epidiorites and amphibolites); on the other hand mica-schists, and 
sheared rocks generally, are conspicuously absent. They include 
(1) ‘basement schists’ on which the altered sediments were laid 
down, and (2) altered basic igneous intrusions, simulating rocks of 
any previous age. All these are older than the granites “by which 
they, and the metamorphic series, are invaded. 
The vertically bedded ‘ironstone series’ is described, and is com- 
pared with similar rocks of the Lake Superior region. They are 
shown to be especially developed along the eastern border of 
Matabeleland, and their conspicuous banding is attributed to re- 
erystallization of fine mechanical sediments under pressure. 
The conglomerate beds (or Rhodesian ‘ Banket’) are 10,000 feet 
thick, and rest unconformably upon the ironstone series in the west, 
both these formations being gold-bearing. But they overlap also 
elsewhere on to the ‘ basement series’; while they are represented 
