174 
POPULAK SCIENCE EEVIEW. 
in South Africa and elsewhere into coke, anthracite, and 
graphite, which are almost pure carbon. Although the chain 
of evidence is here incomplete, this hypothesis has ardent 
supporters in the Cape Colony, inasmuch as the trap-rocks 
above referred to as constituting a main portion, if not all, of 
the Kopjes at Klip-drift are, without doubt, of volcanic origin, 
whether they be dykes or outspread masses, and have passed 
through the fissured strata that here and there in the gullies 
are seen to lie beneath, forming the yet lower foundation of 
the district. 
The low-lying strata, moreover, are known to be. a part of 
the great stratified formation that crops out along the hill-sides 
south of the Orange River basin, in the Colesberg, Smithfield, 
Harrismith, and other districts to the south and east, and 
which, indeed, constitutes all the Interior of the Colony within 
the circling ranges of Namaqualand, the Bokkeveld, Zwarte- 
bergen, Winterhoek, and Zuurbergen, ending near the mouth 
of the Great Fish River in Albany, on the south-eastern coast. 
Within this great area the nearly horizontal and probably 
lacustrine (Triassic) strata, first examined, defined, mapped, 
and described by the late A. Gr. Bain, spread far and wide ; 
and their geological name, “ Karoo Formation,” is derived 
from the Great Karoo Desert, which is a characteristic feature 
of a considerable tract in the Worcester and Beaufort Divisions. 
They are also known as the 6 Dicynodon strata,’ on account of 
the prevalence of the remains of that remarkable two-toothed 
reptile in some of the beds. The Karoo Formation consists of 
an enormous series of shales and sandstones, accompanied by 
some calcareous bands, and rich at places with the wonderful 
remains of the above-mentioned reptile and many others ; also 
with fishes of the palseoniscan type, together with seams of 
lignite and coal, remains of coniferous trees, ferns, and other 
plants. Throughout their whole extent these Karoo strata are 
•crossed by frequent dykes of doleritic, dioritic, and syenitic 
trap-rocks, at different angles, and are often overlain by, or 
intercalated with, similar igneous rock. Here, then, are some 
of the elements required in Dr. Rubidge’s hypothesis of the 
formation of diamond from coal by volcanic interference ; but 
direct proofs are altogether wanting. We see here also the 
reason why many of the Colonists, who have read geological 
books, and observed something of the structure of their country, 
are so ready to suppose that the diamonds are native to the 
spots where they are found — converted, they imagine, out of 
hidden coal-beds and plant-remains by the subterranean heat, 
of which, truly enough, the volcanic rocks bear witness. 
Let us look again at the accompaniments of the diamond 
crystals at Klip-drift and thereabouts ; and although the agate 
