180 A. R. PENFOLD. 



I have to specially thank Mr. F. Morrison, Assistant 

 Chemist, for the usual able and kindly assistance rendered 

 by him in the above detailed investigation, and to Mr. O. F. 

 Laseron, Museum Collector, for the collection of most of 

 the material. My thanks are also due to Mr. E. Oheel of 

 the National Herbarium, Sydney, for his kindness in for- 

 warding the first collection of ^authentic material from 

 his property at Hill Top, 9/11/20. 



PRELIMINARY NOTE ON THE OCCURRENCE OF 

 PORPHYRITIO INTRUSIONS AT YASS, N.S.W, 



By O. W. Mann. 



With Plate X, and Text Figure. 



[Read before the Royal Society of N. S. Wales, October 5, 1921.'] 



OUTLINE, 

 i. Introduction. 



ii. Stratigraphy and General Geology. 



iii. The Porphyries— Evidences of Intrusion. 



iv. Bibliography. 



Introduction. 

 This paper has been written on the evidence collected 

 during excursions to Yass and a subsequent residence of 

 three and a half years in the Yass District, and has been 

 made necessary owing to the fact that, with limited 

 evidence to hand, some geological workers have suggested 

 a volcanic origin for the porphyries. The need for a fuller 

 and more complete account is felt, and the paper is offered 

 as a preliminary to a more extensive work on the same 

 area. In connection with the investigation I am indebted 

 to Professor L. A. Cotton of Sydney University, who has 



