42 
E. DE C. ClAHKE and C. TeiCHE1{T. 
down ill the sec'tiou tlie })ni’:ill('lisni ct-ases. The gTeeuMand-elialk series at 
Gingin rests on sandstones Aviioso age has recently been determined as 
Jurassic (Walkom 1944). BeloAV the Lower Greensand at Dandarragau 
is a series of sandstones (jirobably several hundred feet) of unknown age, 
tentatively assigned 1o tJie Jurassic liy Forman (lOJo). In both sections there 
is an abrupt change in setlimentation from these lower sandstones to the 
greensands underlying the chalk. It would thus seem that these sandstones 
are no-t to be correlated witli the lower sandstone series (Tumblagooda Sand- 
stone and Butte Sandstone) of the Murchison House Series, but are- older, 
aud that no equivalents of the strata below the Alinga Beds are found in the 
south. 
Sandstone which is lithologically similar to the Tumblagooda Sandstone 
occurs in many places lietween Geraldton and Northampton, particularly 
in the \ icinity of Gakabella, on the railway line 20 miles north of Geraldton, 
but no survey of this sandstone area has been made. 
Another area of fairly Avell known Cretaceous stratigraphy, dis- 
covered by liaggfitt (193(1), is situated more than 300 miles north of 
tlie l\riirclii.son Fiver in the (Ardabia Range, south of Exmouth Gulf. 
Stratigraphical and ])a]aeontological information regarding this district is 
still fragmentary, but from published accounts (Raggatt 193G, Crespiu 
1938) it seems evident lliat there is a considerable thickness (up to 800 
feet and perliaj)s more) of chalk, ('ha1ky clays, and marls which underlie 
a greensand deposit witli ammonites of IMaestrichtian age (Spath 1940). 
It Avouid thus seem that much of the ehalky dei>osit is of Senonian age 
(Campaniau aud older) and, judging from foraminifcral evidence (Crespiu 
1938), might also include Tiironiau e(iuivalents. 
From tlie Cardabia Range the t'retuceous extends southward as far 
as- the Gascoyne River where chalk and other rocks have been recognized 
in bores. Nothing is at present knoAvn about the possible continuation 
of this Cretaceous belt along the east side of Shark Bay, but in the 
vicinity of tin* southern end of Shark Bay there are numerous (Aitcrops 
of white shale which undoubtedly represent some part of the Cretaceous. 
That most of the sand plain between Shark Bay and the Murchison RLer 
may be underlain by (h*eta.(*eons sediments will he pointed out beloAv. 
It is thus possible that a more* or less continuous belt of Cretaceous sedi- 
ments extends from somewhere south of the Murchison River northward 
as far as' Exmonth (iulf. 
IV. GEOLOGICAL HISTORY OF THE AREA. 
At stnne time during the koAver or eaily Ui>per Cretaceous an area 
of some relief must have (*xisted east of the area under revieAv, the coast 
running someAvhere ea^t of E. long, A large river fioAving to 
the Avest or Avest-north-west entered the sea, approximately where the 
present lower course of llic IVlurchison is situated, and liuilt up a large 
delta Avhich was gradually pushed Avestward. The size of this delta Avas 
at least 1,099 square miles, though it may have been much liigger. Only 
some pai'ts of the western half of this delta liaA’e been investigated and 
from tin* uniformity and smallness of the sand gi-ain.s one may conclude 
that, when this part was being built, the river furnishing the sediment 
drained a Avide ])Iain suiTounded bv hillv countrv. During this time the 
