GEOLOGY OF ERUPTIVE AND ASSOCIATED ROCKS, POKOLBIN. 407 



basalt, with a second phase of three components, dacite 

 and trachyte, followed by basalt. 



iv. The rocks have been much faulted, the period of 

 disturbance ranging from (?) Carboniferous possibly to 

 Tertiary times. 



It is suggested that the lava extrusions were in the 

 nature of fissure eruptions, the axes of extrusion being 

 roughly meridional, and that this accounts for local modi- 

 fications in the rock types. A penological description of 

 the typical rocks has been given. 



Conclusion. 



Our first geological acquaintance with Pokolbin was 

 made at a University camp four years ago under the leader- 

 ship of Professor David, and we wish to acknowledge our 

 indebtedness to him for kind permission to make use of his 

 maps of the district, for advice as to the general trend of 

 our work and for his kindly and encouraging interest. Our 

 sincere thanks are also due to Mr. W. Eustace Wilkinson 

 of "Maluna," Pokolbin, who at all times generously placed 

 at our disposal his extensive and practical knowledge of 

 the geology of the district. The good people of the district 

 in which our field work lay we always found ready and 

 willing to assist us by any means in their power, a circum- 

 stance which often lightened our labours and added to the 

 pleasure with which we pursued our investigations. 



Explanation of Plates. 



Plate XXV., Geological Map of the eruptive and associated rocks 



of Pokolbin, New South Wales. 



Plate XXVI., Fig. 1. Banded rhyolite, from Post Office Hill, 



showing contortion ( x f ). 

 „ 2. Brecciated rhyolite, Post Office Hill ( x |). 



