62 SECTIONAL ADDRESSES. 
agencies that probably introduced the ores. Many of the claims for the 
presence of metals as primary constituents of igneous rocks are invalid. 
Thus, the oft-quoted gold in the ‘diorite’ of the Ayrshire Mine in 
Rhodesia is secondary.” In other cases the evidence may be wanting. 
The first gold recorded from Kenya Colony was in the nepheline-syenite 
of Mount Jombo, S.W. of Mombasa. The rock appeared quite fresh 
and for thirty-nine years there has been nothing to show that its gold 
was not a primary constituent. Miss McKinnon Wood in her second 
journey to the Kenya coastlands has recently found quartz-lodes con- 
taining copper, lead and zinc in neighbouring rocks; and after that 
discovery there is no reason to regard the gold as an original constituent of 
the nepheline-syenite. 
The distribution of ores indicates their derivation from a layer below 
the igneous rocks. During earth-movements, masses of the subcrustal 
layer are forced upward, while metallic emanations rise up the fractures 
and on reaching the zone above that of the dissociation of water are dis- 
solved in superheated water; the mineral solutions continue the ascent 
till they reach a zone where the ores are deposited in veins or impregnations. 
The primary ores of most metals, other than iron and manganese, 
appear of deep-seated origin ; but after the ore bodies have been exposed 
and attacked by the agents of denudation, they provide the detrital 
metallic particles of placer deposits. Where the rocks are permeated by 
alkaline or acid-charged water, the ore particles are removed in solution 
and thus placer ores are exceptional among the older rocks. Current 
opinion seems reluctant to recognise the extent to which ores have been 
distributed mechanically, and the process has been often disguised by 
their solution and redeposition in situ. In addition to such ores as the 
gold of the Rand, the copper shale of Mansfeld, and the lead sandstone 
of Commern being of placer origin, the scattering of ores in detrital grains 
must have happened frequently and the relics of this process may be more 
numerous than most authorities on ore-deposits are at present prepared to 
admit. 
4. HLiz DE BEAUMONT’S CLASSIFICATION OF MOUNTAINS. 
The deep-seated source of ore-deposits bears on the geology of the inner 
earth, which was exercising geologists in 1831. Appreciation of the help 
that physics and astronomy could give geology is shown by the inclusion 
in the Report of the Association (p. 407) for 1832, amongst subjects recom- 
mended for examination by geologists, of an ‘ accurate examination of the 
conclusions deducible from the known density of the earth, as to the 
solid structure and composition of its interior’; and ‘the examination of 
the visible disk of the moon, with the view of extending our general 
knowledge of volcanic forces’ (p. 410). The-ambition to explain the 
general plan of the earth inspired the early cosmographers, such as Burnet 
(1684) ; but he and his successors in the eighteenth century tried to build 
without bricks or straw, and their theories collapsed when confronted 
with elementary facts. 
After the foundation of Geology at the end of the eighteenth and early 
2. Trans. Inst. Min. Eng., vol. XXXI, 1907, p. 85. 
