4.00 REPORT—1905. 
series of long, thin lenticles of chlorite arranged in lines traversing the slates. 
As the bands of slate are thin it is natural that the indicators should, as a rule, 
run parallel to the bedding; but in many cases, when examined in the mine or in 
sections under the microscope, the indicators are seen to cross the slates obliquely 
to the bedding. 
3. On the Relation between Ore Veins and Pegmatites. 
Ly Professor R. Beck. 
The author gave a summary of the latest investigations on the origin of pegma- 
tites, by W. C. Brogger, H. Rosenbusch, 8. Arrhenius, J. H. L. Vogt, U. Gruben- 
mann, and others. In conformity with these authors, he explained pegmatites as 
products of crystallisation from the superheated water, which remained, after the 
consolidation of a plutonic magma, as a concentrated solution containing many 
of the rarer chemical elements and compounds formerly distributed through the 
whole fluid mass. Tjeing retained in the depths of a plutonic focus under high 
pressure, these remains of magmatic water would pass through a very gradual 
process of cooling; whereas the so-cailed ‘ juvenile’ thermal waters (Juvenile Quellen) 
of similar origin found their way to the upper parts of the earth’s crust, and 
caused there the formation of minerals at lower temperatures and pressures. 
Most ore veins belong to the second class, but a considerable number of occur- 
rences may be’styled metalliferous pegmatites. 
The best known examples of these are found in the group of tin ores, and as 
such were discussed the ore veins of Zinnwald, Graupen, Embabaan, and others. 
As examples of copper ores were cited those of Telemarken in Norway; and 
finally some gold-bearing quartz ree"s were described which are very nearly related 
to pegmatites, and that not merely by their characteristic mineralogical composition 
(Berezowsk, Southern Appalachians, Yukon District, Passagem and other instances 
in Brazil). It may be mentioned in proof of this that certain gold quartzes 
contain tourmaline, the characteristic mineral of all pegmatites. 
4. Magmatic Segregation of Sulphide Ores. By Dr. A. P. CoLEMAN. : 
The formation of ore bodies by magmatic segregation in eruptive rocks has 
long been admitted as regards magnetite and titaniferous iron ores, but the forma- 
tion of sulphide ore bodies in this way has been disputed by many geologists. The 
pyrrhotite ores of nickel in Norway were first recognised by Professor Vogt as 
having this origin; and his theory has been applied to the Sudbury nickel ores 
by various geologists, and opposed by others. ‘he recent complete mapping of the 
eruptive sheet, with which the Sudbury ore bodies are all connected, proves that 
they are really segregated from the eruptive rock and form an integral part of it, 
with every gradation between ore and rock. It is believed that gravitation 
played a large part in the segregation, since the ore bodies are regularly found at 
the lowest points in the lower edge of the norite-micropegmatite sheet with which 
they are connected. 
5. On the Marginal Phenomena of Granite Domes. 
Ly Professor GRENVILLE A. J. Coe. 
In examining the gneisses of the counties of Donegal and Tyrone, which have 
heen in part regarded as sheared Archzean masses, the author was led to conclude 
that the main structures are due to igneous flow, and that the most marked 
gueissic structure occurs where previously foliated sedimentary and igneous 
material has been incorporated with an invading granite. The patches of foliated 
gneiss in the granites of Donegal are thus remnants of considerable masses of 
older rock that have been absorbed ; and the phenomenon of banded gneiss arises 
characteristically as a marginal feature of granite domes. Foliation is found in 
surrounding masses parallel to that in the granite, and at the same time parallel 
