president's address SECTION c. 179 



more recently described by Summers (33), who has shown in places 

 that chert passes into diabase and in other areas is interbedded with 

 normal shales which have been on lithological grounds grouped with 

 the Ordovician. The evidence available suggests that the rocks may 

 be Heathcotian, using that term in the sense of basal Ordovician. 



Bookie. — The rocks of Mount Major, North of Dookie Agricul- 

 tural College, were shown by Ferguson (17 and 22) to be lithologically 

 similar to the Heathcote rocks. Gregory (24) included them among 

 the Heathcotian (Pre-Ordovician) areas. Recently Mr. Summers and 

 myself have examined the area, and intend to publish a note on the 

 relations of the rocks. I may state here that we found clear evidence 

 that the diabase and cherts Avere interbedded, suggesting that they 

 consisted originally of submarine lavas and tuffs, respectively. 

 South of Mount Major cherty rocks containing obscure graptolites 

 were also found. All the available evidence points strongly to the 

 Dookie rocks being of the same age as those of Heathcote. 



Mount Stavely, Western District. — Gregory (24) has pointed out 

 the similarity between the igneous and cherty rocks of Mount Stavely 

 and those of Heathcote. A recent visit to the locality by Mr. 

 Summers and myself has served to confirm the impression, and we 

 noted that the cherts passed gradually into the unaltered shales which 

 have been mapped as Ordovician, although no fossils have been found 

 iti the area. 



The Hummocks. — About 5 miles N. from Casterton, near the 

 western border of Victoria, is an outcrop of a basic rock in part 

 diabasic, in part serpentinous. Its relations to the Ordovician (?) 

 rocks of the district are not clear, but on the flanks of the hill Mr. 

 Summers and I found a bedded cheii: which suggests that we may 

 here also be dealing with another outcrop of Heathcotian rocks. 



A reference to the map (PI. 4) accompanying this paper will 

 serve to show the localities and areas of the rocks dealt with above, 

 while sections (PI. 1) indicate the probable structural relations. If 

 my view of the basal Ordovician age of the Heathcotian series be 

 correct, it may be possible to explain the present distribution of the 

 rocks at the surface, on the view that they only crop out from below 

 beds higher in the series along the axes of much denuded anticlinal 

 folds. If this view is correct the location of these anticlinal areas 

 may prove of considerable help in interpreting the structure of the 

 Ordovician rocks of Victoria, especially in those large areas in Western 

 Victoria from which up to the present no fossils have been obtained. 



Petrological and Chemical Characters of the Heathcotian Series. 

 Howitt (19) has given the most detailed petrographic description 

 of the igneous rocks of Heathcote. Many of the rocks have been so 

 altered that their original characters are hard to determine. Howitt 

 has described diabase-porphyrites, compact diabase, diabase-schists, 

 breccias, and " regenerated rocks," while diorite, aplite, granophyre, 

 and felspar-porphyrite were recoo-nised among the intrusive rocks, 

 and the cherts were described as adinoles. 



