Cretaceous Stratigraphy of Lowtbr Murchison River Area, 39 
Western Australl^. 
nodules vliicli may reach large sizes, measuring sis inches and more across. 
Concentration of chert nodules in the upper half of the chalk was observed 
especially at Toolonga flills, hut farther west at Alinga Point the chalk 
is cherty throughout and chert nodules are numerous in the first few feet 
above the basal iihosphatic layer which is here well developed. 
Fossils, — On the whole the Toolonga chalk is rather fossiliferous 
although the distribution of fossils is very patchy and irregitlar. Fragments 
of Inoceramus shells are ubiquitous, but entire shells are quite rare. As 
a rule the lower half of the chalk is more fossiliferous than the uiq>er, but 
this does not hold everywhere because in some sections, such as west of the 
emergency landing ground, fossils are (juite ijlentiful in the upj)er half of the 
chalk. In addition to Inoceram-us the only common pelecypod is Gnjpliaea 
(^*Pycnodonta^’) ginginensis (Etheridge) which occurs in great quantities 
at Pillarawa and elsew'here. Other common fossils are the brachiopods 
Trigonosemus acanthodes Etheridge and Mogadiiia cretacea (Etheridge), and 
echinoid spines, probably belonging to Cidaris comptoni Glaueif, of which 
a few interambulacral plates were also found. Very important members of 
the chalk fauna are Mars}i piles and Uintacrimts whose detached plates are 
locally very numerous. Of the former genus there are two distinct types 
of calicular plates: one resembles the common Marsupites testiidmarius 
(Schloth.) of the Northern Hemisphere, both the smooth and the ribbed 
variety being present; the second ty])o of plate is considerably lai'gcr and 
indicates a calyx about twice the size of that of mature specimens of 
M. tesfudinarlus. These plates are always smooth. They might well repre- 
sent a new species of this interesting genus. Foraminifera are abundant 
but have not yet been studied. 
Following is a list of the non-foraminiferal fauna (preliminary deter- 
minations only) : 
Cidaris compt&ni Glauert, Marsupites testuddnarius ( Schlotheim) , 
Marsupites nov. sp., Uintacrinus sp., Serpula gregaria (Etheridge), Trigono- 
semus acanthodes (Etheridge), Magadina cretacea (Etheridge), Grijphaea 
ginginensis (Etheridge), Inoceramus sp., Ostrea sp., Sx)ondgliis sp., hclemnite 
fragments, Scilhdepas ginginensis (Etheridge) . 
Thickness. — The gi’eatest thickness of chalk, 320 feet, was measured 
just west of Jannawa, a small residual hill north of Pillarawa (text %. 13) ; 
of this thickness 20 feet is dnricrust and wc do not feel quite certain that 
part of this might not. consist of altered Second Gully Shale. However, 
even in that case the thickness of the chalk cannot be less than 100 feet. East 
of the telegraph line the thickness of the chalk is slightly more than 00 feet, 
but west of Pillarawa it decreases to little more than 35 feet at Toolonga 
Hills. Farther west it increases again to 55 and G5 feet at and near Thirin- 
dine. In Second Gully the thickness is again less (25-35 feet), hut at 
Alinga it has increased to 55-60 feet. At Meanara there are about 70 feet 
of chalk. 
7. Second Gully Shale. 
Derivation of name. — Second Gully is the name of the valley of one of 
the northern tributaries of the Murchison River about three miles from 
