38 
E. DE C. Clarke and C. Teichert. 
seen in a few places where this hard crust has been removed. North- 
west of the Murchison Kiver the chalk can be followed along the whole- 
length of the scarps from Mullewa Point in the west to a place about 
one-and-a-half miles east ot the telegraph line and the outcrops are 
generally very good (Plate 1). There is much slumping in the chalk, 
mainly owing to the slippery nature of the underlying Alinga Beds. 
The result is that in places the entire slope of the escarpment down 
almost to the top of the Tuinhlagooda Sandstone is covered Avith slumped 
chalk (text hg. 13). The eastern limit of the Tuolonga Chalk has not 
Text Pig. 13. 
Looldng south at the scarp of the upper part of the Murchison 
House Series from the site of section 3 near north end of Plate II., 
with Jannawa and PiUarawa Hills in the middle of the picture. 
yet been determined. xVs seen from the air a conspicuous belt of thick 
scrub Avhich chai'acteri/.es the lop of the chalk scarp, bends sharply to- 
the north-east east of the telegraph line; it is most likely that this marks 
the edge of the chalk outcrops. Parther east remnants of the chalk may 
occur in 2 )laces as, for example, in the durierust which coA^ers the Alinga 
Beds on top of the escarpment just north of Weerinoogudda Dam, about 
nine miles N.N.E. of the (‘astern end of the area of our surA'ey. South 
of the Murchison Kiver small outcrops of the Toolonga Chalk occur on 
the north side of ^Mcanarva Hill. 
Scope . — The Toolonga Chalk forms an exceedingly avoII defined zone. 
Its loAver boundary is rarely Avell exposed, but when seen (as in text fig. 
12), seems to be sharp, though sometimes someAA’hat undulating. In the 
eastern half of the area mapped the chalk forms the top of the scarp 
north-Avest of the Murchison Kiver, ])ut in the Avest it is overlain by 
shales (Second dully Shales). The boundary is rarely exposed, but in 
general the transition from the chalk to the shales seems to he rather 
sudden. 
Lithology . — Lithologically the Toolonga Chalk is rather uniform 
throughout the entire area. It is a yelloAvish-Avhitc, massive, usually 
rather coherent rock Avhich, however, AA'eathers easily on the surface. At 
its base it contains in many places a layer of phosphatic nodules, usually 
not more than six inches thick. The nodules themselves are of irregular 
shape and are often geode-like, Avith chai’acteristieally cracked surfaces. 
The lower part of the chalk above the phosphate layer is as a rule very 
pure and Avhere fossils occur they are Aisually more numerous in this 
loAver part. In many places the upper part of the chalk is rich in chert 
