174 G. A. Cook: 



and the valleys widen out. The pre-basaltic Merri was a mature 

 stream, and did most of the work in the peneplanation of the 

 area. After, however, the outpouring of the basalt it was rejuve- 

 nated, and now in the Northern area is rapidly cutting down into 

 the basalt, and into the Silurian in places towards the South. 



There is also evidence in the area of the Merri having changed 

 its course in recent times. Just North of the Pentridge Stockade, 

 on the North bank of the Merri a recent alluvial flat occurs. 

 Through this flat a creek meanders, which may be termed " Falls 

 Creek." From its headwaters down to the alluvial flat this creek 

 is verv young; in fact, it enters the flat over a waterfall formed 

 by a bar of Silurian rock. In all probability the Merri Creek, which 

 now cuts across the South boundary of the alluvial flat, formerly 

 flowed right round its Northern boundary. This would account 

 for the sudden change in the grade of Falls Creek. This change 

 of course of the Merri is post basaltic in age, for the alluvial flat 

 contains occasional boulders of Silurian and of basalt. 



Stratigraphy. 



Silurian. — This series consists of the fine sandstones and shales 

 of the Melbournian division of the Victorian Silurian. South of 

 the Hell Sheet bridge a river cliff section shows a very good ripple 

 marked surface on an exposure of one of these beds. The hollow* 

 average three inches in diameter. 



Xo fossils were found in these rocks. The beds are only folded 

 to a medium extent, giving a general strike 10 dcg. Fast of North, 

 and the dips in general are about .'50 deg. In the area studied the 

 beds usually dip to the West, but occasionally a small anticline and 

 syncline occur, giving a few minor Easterly dips. The preservation 

 of the North and South ridge to the Fast of Kails Creek is probably 

 due to the compression of the rocks caused by such a local pucker. 

 This method of preservation is also exemplified by the Silurian ridge 

 North of the Coburg Cemetery. The road section just to the West. 

 of the cemetery shows a somewhat complicated pucker in the Silu- 

 rian, which pucker can Ik- traced South over Hell Street. In this 

 connection it is significant that these two ridges have a North and 

 South direction, i.e.. a direction parallel to the strike, and to the 



major fold axes of the rocks. 



The Silurian also shows evidence of faulting in a North and 

 South direction. In the bend (concave to Pentridge) of the Merri 

 just North of Pentridge, Silurian outcrops in the bed of the stream. 



