CkETACKOUS STliATlGliAPHA' OF LOWFR MUKCIIISON KiVER AeEA, 41 
\Ve STE HN AuST 11 a lia . 
Litliohxjji . — As I'ar as (•<)ul(i !)(.* ast-artaiiual the lithology of this shale 
is very uiiilonn throughout the area of its oecurreuce. It is a very fine 
glaueonitic shale which seems to be devoid of any admixtures of other 
rock types. 
Fostyils , — Xo fossils were found in this shale st'ries. 
Thivimexfi . — The greai('st thicknesses of the Second Gully Shale were 
measured at Aliiiga (7o feet), along the east side of Second Gully near 
the Butte (92 feet) and north of Thirindine (80 feet). From here the 
thickness decreases eastward owing to the general rise of the strata in 
this direction. It was not observed anywhere east of Toolonga Hills. 
At ^leanarra Hill, south of the Murchison Kiver, about 45 feet of the 
Second (Jully Shale are pi*eserved. 
H. Auk axu Goruklatiox of the iMriuuiisox IlorsE Series. 
The only i)art of the Murchison House Series which can be accurately 
dated by means of fossils is the Toolonga CTialk. The occurrence of 
and riiitacrhius characterizes it dehnitely as an e(iuivalent of 
t]i(‘ Santonian stage of the Fi^Jcr Cretaceous. 
As to the remainder of the se(juence, more particularly the various 
sandstone and shale series below the chalk, no definite conclusion can bo 
drawn. From general considerations of the nature <4' these sediments it 
seems, however, unlikely that strata of an earlier age than Cretaceinis are 
present. Tlte whoh‘ sei|uence of rocks is conformable ami there are no 
major hreaks in the sedimentation ju'ocesscs. On the wlioh* there is a gradual 
change freiii i oarse-grained m-ar-shon* to tine-grained off-shore sediment«. 
The total (^x'i)osed thi<'kn(‘ss of beds below the chalk is less than 790 feet to 
which must be addcal an ludviiown thickness of I'ocks below tlie low^'St ex- 
posed beds of tile Tiimblagrjoda Sa!id>t(>ne. ]lowev(‘r, lliesf* lower sand- 
stones must have be(m dot)osit(Ml faii'ly rapidly and the time rcpres(‘nted by 
them cannot lie \(’ry long. 
From sucli general consichu’atioiis it might ))e concluded that sediment- 
ation in the area began ju-obably not before tlie lieginning of Ulipor 
Cretaceous time and ceilninly not eai’livr than some time in tin* Lower 
('ndaceous. 
Contemporaneous deposits are widespread in M^estern Australia in a 
coastal belt betw('cn about 22*^ and S. hit,, seldom extending more than 
fifty miles inland from the shores of the Indian Ocean. The Tooloinra Chalk 
can (easily b(‘ (‘orrelaled with litliologically similar deposits at Gingin and 
at nandarragan, 00 and 100 miles north of Perth. (‘Iialk de[)osils occur 
in these placi's with a maximum Ihickiies.s of about 70 feiT, carrying a fauna 
idcntii'al with that of th(‘ Toolonga Chalk. However in both places ihc 
tliickncss of the ('I'ctaceous lagL is smaller and the whole sequence ap- 
imrently mucli less com])Iet('. Both at Daiidarragan and at Gingin the chalk 
is sandwiched between green>nnd^; a l.owcr Greensand which is 20 feet 
thick at Gingin and up to 70 feet at Dandarragan, and an Tapper Gr(‘ensand 
of which 140 feet are exi'osed at Gingin and less at Dandarragan (see 
Clarke, Teichert, and Pridcr, 1944, p. 274. and Teichert and Matheson. 1944, 
p. 168). The TAnv('r Greensand is most ])ro})ably contfmpioraiu'ous with the 
strongly glancoiiitic Alinga Beds of the iMurchison TTonse Sicries, but fartlier 
