AT THE CAPE OF GOOD HOPE. 
299 
more deliberate investigation, by a more cautious observer, would 
also, I think, lead to similar conclusions. If he were one desirous to 
explain all geological phenomena by the agency of water, and be 
therefore disposed to consider the mixture of schistus and granite as 
resulting from cotemporaneous formation, he would hesitate over 
the imbedded masses of the former uncontaminated by their matrix, 
and would be still more perplexed by the fact that they can be sepa- 
rated without mixture. He would in vain seek in them those 
instances of the wedging of one rock into the other, which has been 
supposed confirmative of this opinion.* In looking at the principal 
line of junction between the granite and the schistus, he would see no 
gradual gradation of one into the other, but a distinct, though inter- 
rupted line of separation. This interruption he would find to be occa- 
sioned by veins of granite passing directly from the principal mass of 
granite into the schistus ; in other words, the subjacent rock shooting 
into the superincumbent one. f Below this line he would indeed find 
an intimate mixture of the two rocks, occasioning a compound of a 
lighter colour than the schistus ; such an appearance as might in itself 
be explained on the supposition of coeval formation. But he would 
meet a fact exceedingly unfavourable to this conclusion on a closer 
view ; he would see here, as in the granite, two pieces of schistus of 
* “ The substance of the vein is to be observed mixed with and passing into that of the 
rock; and it wedges out in every direction in the mass of the rock, thus showing that it 
has not been filled from above or below, but is, as it were, a secretion from the rock 
itself. Such veins are denominated cotemporaneous , because they appear to have been 
formed almost at the same time with the rock in which they occur.” — Elements of 
Geognosy, p. 236 . 
f “ It is an incontrovertible fact, that no veins of the substance of a subjacent rock ever 
shoot into a superincumbent one ; because the structure of the crust of the globe, from 
the oldest granite to the newest alluvial deposit, shows that veins are composed either of 
the finer substance of the rock in which they are contained, as is the case with those veins 
denominated cotemporaneous, or of substances more or less different from the rock, 
and which are frequently connected with mountain-masses or beds that lie over those 
rocks by which these veins are traversed. Thus no veins of granite are ever observed 
shooting from the oldest granite formation into the superincumbent gneiss ; but veins of 
gneiss traverse through granite.” — Elements of Geognosy, p. 237. 
Q Q 2 
