792 GENERAL GEOLOGY OF MARULAN AND TALLONG, N.S.W., 



On its eastern boundary the intrusive rock is coarse, on its western 

 boundary it graduates into a fine-grained porphyritic phase. Near 

 the western margin are very numerous and extensive *' Daly- 

 masses," the size and abundance of these stoped portions decreas- 

 ing as we pass eastwards. It seems probable that the plutonic 

 mass has the form of a somewhat sill-like mass with an underlay 

 to the west, and that portions of the original roof still exist on 

 the western side. 



By the above statement I do not wish to imply that the grano- 

 diorite forms a sill in the ordinary sense of the term. Its 

 junction with the sediments is much too irregular to support any 

 such theory. It seems, however, to have forced its way surface- 

 waids in a general way conformably with the westerl}' dip of the 

 Silurian rocks. If this interpretation is correct, the igneous 

 intrusion differs from any of those types mentioned by Iddings, 

 in his })aper on " Bysmaliths."^' 



The age of the granitic rocks cannot be deter- 

 mined with very great accuracy. They are certainly Post- 

 Silurian, and certainl}"^ Pre- Per mo-Carboniferous. To the south 

 of the area dealt with in the present paper, rocks of Devonian 

 age occur at Windellama. These are apparently conformable 

 with the Silurian rocks. It is probable that the Glenrock grano- 

 diorite is Post-Devonian. If so, it must belong to some part of 

 the Carboniferous, during which time the injection and extrusion 

 of acid eruptive rocks was extremely active in Eastern Australia. 



Wingello Basalts, 



These rocks have not been studied in detail in the present 

 contribution. Jaquetf has mapped and described them to some 

 extent. For the most part, they form flows tilling in shallow 

 vallej^s of Tertiary age. The contact between them' and the 

 underlying Permo-Carboniferous sandstones is marked in places 

 by intense silicitication of the latter rocks, which have been 



* Iddings, J. P., "Bysmaliths." Journal of Geology, vi., 1898, p. 704. 



+Jaquet, J. B., " The Iron-ore Deposits of New South Wales." Memoir of 

 Geol. Survey of N. S. Wales. 



