Cretaceous Stratigraphy of Lower Murchison River Area, 
Western Australia. 
35 
L Thirindine Shale. 
Derivation of name . — Thirindine is the name of a prominent point in 
the scarps north-west of the Murchison Kiver, due north of Yalthoo Wind- 
mill. 
Areal distribution and outcrops ,— Thirindine Shale crops out all 
along the scarxis north-west of the INIurchisou River. It can he traced almost 
without interruption from Second Gully Point in the south-west to a i^oint 
about one and a half miles east of the telegraph line where the outcrops dis- 
api)ear under the vegetation cover and have not been traced farther east. 
In 1943, however, the junior author located an extensive outcrop area of 
these shales in the vicinity of ^Veerinoogudda Dam, about eight to nine miles 
farther X.X.R., whence it continues for a distance of about six miles to 
the south-east along the track to Warrfinjal)abba Siu'ing as far as a point 
about SIX miles north-east of Mt. Curious and about four miles north of 
Bungabaiuly Creek, near the eastern boundary of ^lurdiison House Station. 
Prom the air it can be seen that good outcrot>s of the shale extend X.E. and 
E.N.E. of Weerinoog^udda Dam for a distance of three to four miles. In 
the west, the Thirindine Shale is absent west of Second Gully Point and in 
the interior of Second Gully, l)ut south of the IMurehison River small patches 
were found on the north side of IMeanarra Hill. 
Scope . — The Thiiindine Shale is always easily recogonizable because it 
weathers with a whitish surface. Its lower boundary is mostly fairly well 
defined, although in certain ]»laces there is a transition zone, one or two feet 
thick, from the underlying Butte Sandstone. The upper boundai*^' against 
the glauconitic Alinga Beds is mostly quite sliaiq^. 
Lithologp . — The Thirindine Shale is a very tine-grained dcfiosit, usually 
of greyish colour. In | laces it consists of alternating softer and harder 
layers, the latter usually being whiter. However, the softer, greyish layers 
also harden 4)n exposure and form a whitish surface. This surface-harden- 
ing causes the Thirindine Shale to be less easily ei*od(>d than the softer sedi- 
ments above and below, so that it forms a characteristic teiTace in the jirofile 
of the slopes along which it crops out. 
In some x:)laces, the shale contains some glauconite. This is particularly 
marked in the scarp on the north-east side of Second Gully where its glau- 
conite content increases gradually upwards so that there is a transition to 
the overlying glauconitic Alinga Beds. Glauconite was also observed else- 
where in the Thirindine Shale, for example in the Toolonga Hill section, 
but it is usually subordinate. 
Fossils. — Remains. of fossils were found only in the lower part of the 
shale at Toolonga Hills, where hard bands contain cavities left by belemnite 
guards which have been dissolved by eirculating waters. In places where 
the shale is glauconitic a peculiar vermicular structure of the senliment was 
observed which is believed to be due to tlu' action of mnd-burrowiug organ- 
isms, probably worms. 
Thickness . — The thickness of the Thirindine Shale varies greatly. In 
the east, east of the telegraph line, it is 18 feet thick, and just west of the 
line, near the emergency landing ground, it c^ecreases to five-and-a-half feet, 
