EUBIDGE — SOUTH-ArEICAX EOCKS. 
53 
It is well kuown that prehnite is a common mineral in some parts 
of this colony. It occurs in the dioritic or syenitic dykes of the 
Dicynodon strata, and is evidently a product of the re-arrangement of 
the minerals of these dykes during their decomposition. The prehn- 
ite is found in laminae between the decomposing masses of the dykes 
and on their faces as digitate concretions. Unlike M. Daubree's 
zeolites it has not required heat for its formation, but, like them, it 
is forming at this hour by aqueous action. I have almost as little 
doubt that dykes and other masses of granite are forming in the same 
way from the re-arrangements of the constituent minerals of the 
gneiss. I find it easier to feel the truth of this on the spot than to 
convey it to others ; still I will endeavour to give some reason for 
my faith. One mass of gneiss, near Henkrees, in which a vein of 
granite, terminated by an expansion about a foot square, proceeded 
along the gneiss. It was quite evident that there was no intrusion, 
no connection with any mass below. Spindle-shaped masses of 
granite placed between beds of felspathic, micaceous, and other rocks, 
were numerous and could often be entirely removed by a hammer, 
showing they had no connexion with any subterranean mass. 
Spherical lumps of granite or syenite were frequently quite isolated 
in the schists of the mines. I have stated before that beds of quartz- 
ite appeared to be intercalated by a filtration from above ; some of 
these could be traced down till they became mixed with mica and 
then with felspar, and not very much deeper assumed the character 
of the gneiss of the country. Other masses, which seemed to be in- 
termediate between these, toward the spindle-shaped granite lumps 
above, were composed principally of quartz, with a few grains of mica 
and felspar, and occasionally garnets : these were surrounded by mica- 
schist in henf-up strata ; yet the whole mass, perhaps twenty pounds 
or less in weiglit, could be removed. These circumstances seemed 
to me to prove clearly that if felspathic rocks of any kind are the 
products of metamorphic action, then are granite, syenite, etc., trace- 
able to a like origin ; that if, as I think, I liave clear evidence, in the 
Maitland Mines and other places of this neighbourhood, palaeozoic 
rocks are convertible into micaceous, chloritic, and felspathic schists, 
without evidence of eruptive agencies, then are the so-called igneous 
rocks equally so. I think it will scarcely be disputed by any who 
admit the re- arrangement of felspathic rocks I have contended for, 
that causes by which such re-arrangement was made, may have 
efi'ected the original conversion of sedimentary into crystalline rocks. 
AVe have in this province a rock which has been pronounced decidedly 
igneous by the highest European authorities ; it is the claystone- 
porphyry of Bain. Yet its position among the other rocks is, in 
many respects, just that of the quartzite ; and, like the latter rock, 
its individual beds and its minor masses are conformable with the 
stratified rocks, while in ranges many miles in length, it crosses the 
strike of the strata, generally at an r. igle of about 30°. This fact 
was first demonstrated to me by Mr. Pinchin, a gentleman who has 
made many interesting observations on the geology of this country. 
