54 
TUE GEOLOGIST. 
The sections of the Zeurberg, of Yan Zonder's PLiin (given above) 
on the Graff Eeinet road, together with a somewhat imperfect re- 
collection of that of Graham's Town, had led me to believe that the 
relation of the porphyry to the slate was constant. It is now evident 
that I was in error here. The fact of the masses of the porphyry 
crossing the slate without disturbing it seems to me greatly to 
strengthen my views as to its metamorphic origin by rendering the hy- 
pothesis of Messrs. Bain and Wylie untenable. The former gentleman 
supposed that the porphyry had been poured over the surface of the 
strata as liquid lava. Mr. Wylie referred its origin to volcanic ac- 
tion, producing ash, which was deposited at the bottom of the ocean, 
and formed this igneous-like rock with its contained granite pebbles 
arid fragments of rock. The fact of the direction of its masses being 
at an angle of 30° with the strike seems to me to be incompatible with 
either of these hypotheses. The ranges of porphyry, like those of 
quartzite, die out and reappear. The normal position of the porphyry 
appears to be as in fig. 4, but I have seen it placed as in figs. 5 and 
6:— 
Slate. Porphyry. Slate. Slate. Porphyry. Slate. Slate. Porphyry, Slate. 
The character by which we all agree to recognize this rock is the 
presence of m.asses of quartz and granite of various sizes with occa- 
sional fragments of slate and other rocks. Sometimes these masses 
are as much as fifty pounds in weight, at others they are so minute 
as to be scarcely recognizable by the naked eye. In a recent journey 
to Paardenpoort I met with a mass of this porphyry which terminated 
in a vein about a foot thick, with very minute crystals. jN'ow what 
is the^character of the rock among which this porphyry is interposed 
or interstratified ? It is such that no one acquainted with the two 
would pretend to diagnose them, save by the presence of the crystals 
above mentioned. Nor would the blowpipe, or even more careful 
analysis, so far as I am aware, enable him to do so. If then the base 
of the rocks differ so little, and there is evidence that no displacement 
has taken place in any known section (see Bain and Wylie), is it not 
clear that this rock has originated in slow conversion ? Yet I be- 
lieve whatever may be predicated of it may be equally so of granite ; 
for it contains granitic masses in great numbers, and often of large 
size : besides granite, veins occupy precisely the same position among 
rocks which I have given reasons for believing to be the same strata 
in the Western Province. 
But it will be seen above that I am not disposed to admit that the 
evident displacement of strata is at all times due to eruptive agency. 
I have given instances, on a very small scale, in which 1 feel sure it is 
not so. I hope ere long to be able to show that the infiltration of 
quartz from above has produced this- effect, but my evidence on this 
