Sedimentary Rocks. 65 



Dicranograptus nicholsoni, Hopkinson. 

 Dicranograptus -furcatus, Hall, or zic-zac, Lapw. 



The " purple grey shales " at the mouth of Riddell's Creek 

 are at the locality Ba 67, and are Upper Ordovician. 



(b) Lancefield Junction, south and west of Jackson's Creek. — 

 We have already mentioned the Grit hills which lie between 

 Lancefield Junction and Evans Creek. Two ridges, composed 

 of Grit, run almost north and south, converging towards the 

 south. Each ridge represents a massive band, or series of bands, 

 of grit, with fragments of which their summits and slopes are 

 littered. The strike of the more westerly bands is about N. 20°W., 

 and the dip east, so that the convergence of the two ridges is 

 probably due to an actual convergence of two bands of grit, or 

 of the same band on opposite limbs of a syncline pitching north 

 from Evans Creek. If this view be correct, the western limb 

 would be represented by the faulted band in Jackson's Creek, 

 while the eastern limb would be indicated by the low outcrop 

 exposed east of this, the limbs being represented by the 75°E. 

 15°N., and the 75-85°W., 12-15°S., of QS. 6 SE... Such a pitch- 

 ing syncline would also explain our failure to find Grits between 

 Sunbury and Evans Creek. In the small creeks which drain 

 these Grit ridges bed rock is rarely exposed, with the exception 

 of the more prominent grit bands, but in a few places the streams 

 have worn down on to brown rubbly mudstones or shales. One 

 such outcrop directly between the two ridges, and on our sup- 

 position above them, yielded Diplograptus. 



Near the head of Evans Creek Grits outcrop also. The strike 

 is N. 6°E. They are not seen in contact with the Dicellograptus- 

 Nemagraptus shales downstream, which appear unconformable 

 with them and below them. A north and south continuation of 

 these last bands would take one to the " quartzose grits " on Jack- 

 son's Creek (QS. 6 SE.), and to the Grits of Mount Tophet and 

 The Gap. 



The area between the Jackson's Creek section described in 

 (a), and Evans Creek, represents the largest continuous ex- 

 posure of Riddell Grits in the district. A study of QSs. 6 SE. 

 and 7 NE., or of the military map of Sunbury, will show the 

 two ridges running south towards Evans* Creek, separated by a 

 north and south valley. Following the creek south from Lance- 

 field Junction, all the rocks exposed in its bed as far as due 

 west of the 28 mile post on the railway are Dicranograptus shales 



