The Contact Between the Cranitic Bocks and the (\vrdi'p Series 
AT Arhadale. 3T 
The westei'u stri|) of the area is oeeupied by the sedimentary roeks of 
the Cardup Series. These rocks strike parallel to the o-ranite gneiss- 
sediment contact and dip (on the average) 60° to the west. Ti-averslng this 
series in a westerly direction from the contact the succession is (luartzite 
(with fine cherty bands), sandy slate, tine white slate, dark greyish to blai'k 
caibonaceous slale^ and tine whit(‘ slate (lliese I'ocks ar(‘ leferred to as slates 
but they are little more than shales with a vtu’y jujorly developed fracture 
cleavage). A few exam})les of graded bedding were noted in tlie section 
exposed along the Bedfoi’dah' Hoad at the south end of tlie area and reailings 
taken here indicate that the, older beds lie to the east, i.e., that the sequence 
is normal and not overturned. Tlie actual contact with the granitic gneisses 
is only \'isibh‘ in one jilace (on the roa^l at tlie south end of the ar<‘a) but 
it can be Jixed within several yards over the remainder of the area and the 
succession of beds is everywhere tlie same. The Cardup sediments are best 
exposed in the quarry at the south-western corner of the area (whex'e the 
slates have been quarried for brickmakiiig) and are seen t<» be slightly drag- 
folded and traversed by numerous minor faults with displacements of several 
inches. The nature of this minor faulting and drag-folding will be more 
fully described in the following section dealing with the structure of the 
area. 
The Cardup Series is cut by a number of doleritic dykes which may be 
traced from the granitic rocks into the neighbouring sediments. From the 
geological plan of the ai’ea (Plate 1) it will he seen that the dolerite dykes 
appear to have been intriuhni along a definite set of fractures which extend 
from the gi’anilic rocks into the sediments. In one place (on the Avest wall 
of the slate quarry) gi'oenstone has been intruded in the form of a sill in 
the sediments and has produced sliglit contact alteration of the slaty roedvs. 
No such contact effects Avere noticed along the gneiss-sediment contact. 
From the field occurrence the chronological order of the roeks exposed 
in the area maiJjied ai>pears to l)o; — 
Youngest. (8) Minute barite veinlets in the dolerite on the east face 
of the slate quarrA\ 
(7) Dolerite dykes. 
(6) Plpidiorite sill in Cardup slates. 
(5) Cardup sediments ((juartzites, sandy slate, white 
slates, black carbonaceous slates, Avhite slates). 
(4) Qiuu’tz veins in gneisses. 
(3) A|)logTanite intrusions. 4 Fine banded granitic 
> gneisses, exact relation to 
(2) Hybrid augen gneisses. ) (2) and (3) unknown. 
Oldest. (1) Hiotite-epidote-horiiblendo hornfels and quartz (? 
(qiartzite) xenoliths hi the hybrid ang(Mi gneisses. 
(2) The Geological Structure. 
Mapi)ing of all of tlie axailable minor structures of the exposed rocks 
has yielded a considerable amount of information regarding th(‘ structure of 
the area (and of the Darling Scarji generally). The hybridised gneisses 
of the eastern section shoAV minor folding in a nuudier of places but no con- 
stancy in the orientation of these structures could l)o found, as Avill be 
readily understood after an examination of the exposures in the Roads. 
Board quarry, where the gneisses are seen to be in xenolitlhc lilocks, irregu- 
