NEPHELINE-BEARING ROCKS. 177 



Some months later on examining a collection of rocks 

 given by Mr. Eustace Wilkinson of Pokolbin near Maitland 

 to Mr. R. E. Priestley, F.G.S., a similar porphyritic rock 

 was found, and, on sectioning, abundant nepheline was 

 clearly visible. In letters from Mr. Wilkinson I learn the 

 following particulars : The rocks occur in a large series, 

 stretching from Stewart's Brook to the Barrington Trigono- 

 metrical Survey Station, a distance of 10 miles. They 

 appear everywhere to overlie a dense normal olivine basalt, 

 and this in turn overlies steeply dipping cherts, sandstones, 

 and shales, carrying such typically Carboniferous forms as 

 Orthotetes crenistrla, Spirifera striata, Orthonychia, 

 Capulus cf. Oehlerti, De Kon., with abundant crinoid stems. 

 The fossils were kindly determined by Mr. W. S. Dun in 

 specimens forwarded by Mr. Wilkinson. 



The section exposed on the Barrington Trig, as observed 

 by Mr. Wilkinson, is shown in fig. 1. He remarked, how- 

 ever, that it was drawn from memory, and that it had been 

 possible to devote but a short time to its examination. And 

 further, that as it was chiefly rocks of rather unusual 

 appearance that he collected, normal basaltic rocks were 

 sometimes passed over. Nevertheless he is emphatic on 

 the highly important observation that the coarse-grained 

 dolerites overlie normal olivine basalts. 



A final visit proved that rocks of this type occurred near 

 Nundle. They cap Square Top Hill, which lies three miles 

 to the west of the township, and under the microscope 

 prove to contain abundant nepheline. 



There is evidently here a field of great extent geographi- 

 cally, (Stewart's Brook and Nundle are more than forty 

 miles apart), and of considerable interest petrographically, 

 see fig. 2. In view of the writer's approaching departure 

 for England, it was thought well to collect into a brief note 

 the scanty data available on these rocks to direct attention 

 to their occurrence. 



L— August 2, 1911. 



