Bocks near Heathcote. 343 



coarse coiifjlni aerates containinrr diiubase fragments would occur. 

 None such have, however, been found. 



The irregularities in the surface boundaries between Ordo- 

 vician and diabase, and the more or less inconstant development 

 of black cherts along the junction, as sho^\^l on the maip, are 

 features some of which Jiire, I think, due to a misinterpreitation of 

 the field evi,dence. Some, however, are real, and I think thej' 

 can be explained on the view that submarine vulcanicity started 

 in Lower Ordnviciain times, that a mixed series, consisting 

 largely of unbedded and bedded tuffs and lavas, with relatively 

 minor intrusions, was developed, and passed gi'adually upwards 

 into more normal sediments. There would be developed irre- 

 gularities in thickness in the diabase series, and on subsequent 

 folding and denudation the present more or less embayed 

 junction between Ordovician and diabase would be produced. 



The evidence as yet available of the relations of diabaise and 

 Ordovician is not, I think, so clear as to enable a positive state- 

 ment of the Ordnvician or pre-Ordovioian age of the diabase 

 to be made, but for the reasons given aibove I am a.t present 

 inclined to group it with the Lower Ordovician sediments 

 rather than as forming a distinctly pre-Ordovioian series. 



(e) Physical Geography of the Lower Ordovician Period. — 

 Professor Gregory' has given an interesting sketch of the prob- 

 able relations of land to sea in Lower Ordovician times, based 

 on his view of the pre-Ordovician aige of the cherts and diabases. 

 He correlates with the Heathcote rocks outcrops at Lancefield, 

 Dookie, near Geelong, etc., and maintains thait a barrier of pre^ 

 Ordovician land stretched across what is now Victoria, eastwairds 

 from a more or less X. and S. line from near Geelong through 

 Heathcote to Dookie. These places, accordintr to Professur 

 Gregory, lie along the eastern marsrin of the Lower Ordovician 

 sea, and define the e-vsterly boundarie'S of the Lower Ordovician 

 beds. 



Holding a« I do a different view of the origin and age of the 

 cherts and the diabases, I am unable to agree with Professor 

 Gregory in this sketch of the Lower Ordovician boundaries. In 

 my opinion there are no good grounds for regarding the present 

 eastern boundaries of the Lower Ordoviciam series as marking 

 their most easterly development in Victoria. I regard the cherts 



