76 Harris and Crawford: • 



-cated as the boundary of Lower and Upper Ordovician, must 

 jjass right through the township. 



XI. — Newer Volcanic. 



It is not our intention to deal with these rocks in detail. On 

 'examination they will probably be found to present problems 

 not indicated by a cursory inspection. Where the basalt flowed 

 •over the old water sheds, the covering is comparatively thin. 

 In the valleys it is of considerable thickness, as is well shown 

 between Gisborne and Dalrymple's and west of Lancefield Junc- 

 tion. Below the " Toolern Fault " the thickness is greater and 

 bedrock is not exposed by the Toolern, Tangadook or Kororoit 

 •Creeks in the south of the district. 



XII. — Summary. 



1. Attention is called to the comparative neglect of a com- 

 plex and interesting area within 30-40 miles from Melbourne. 



2. The Geological Survey classification of rocks in the Gis- 

 borne district is set out, and a revised classification proposed, 

 -dividing Upper and Lower Ordovician, substituting the Kerrie 



Conglomerate (already recognised by Victorian geologists) for 

 the Oolitic, and adding a new series, the Riddell Grits. 



3. The physiography of the area is briefly touched on, and 

 the influence of the Djerriwarrh Fault and the Newer Volcanic 

 basalt flows indicated. An attempt is made to re-construct the 

 main outlines of the pre-volcanic topography. 



4. The distribution of Lower and Upper Ordovician rocks 

 is described, and some account is given of their graptolite fauna. 

 It is shown that the division between Lower and Upper Ordo- 

 vician is a straight line running through Gisborne in a direction 

 slightly east of north, and evidence is adduced to show that this 

 line represents a fault which is indicated on the accompanying 

 map as the Djerriwarrh Fault. The down throw is to the east, 

 and the fault is pre-Newer Volcanic, but how much older is un- 

 known. 



5. A tentative recognition of three Upper Ordovician grapto- 

 lite zones is proposed — 



1. Diplograptiis-Didymograptus zone (Lowest). 



2. Diccllograptus zone. 



3. Dicranograptus zone. 



