108 PROCEEDINGS OF SECTION C. 



at the hands of thoughtless visitors, and good specimens which were 

 exposed to view have been defaced or removed. The owner of the 

 property has wisely prohibited the removal of any more specimens. 

 Good examples of the leaves from this spot are in the Yass Mechanics' 

 Institute and the Mining and Geological Museum, Sydney. 



Jerrawa Shales. — ^The ban"en character of the Jerrawa shales 

 has already been commented on. To say, however, that all the sedi- 

 mentary rocks to the west of the Gunning- Oolong granite are barren 

 would not, strictly speaking, be true, as the shales between the 

 granite and Jerrawa Creek give some good farming and grazing land. 

 The character of the soil in this part of the section is very similar 

 to and may prove to be part of the Gunning shales. The typical 

 barren Jerrawa shales cross the railway line near where the Jerrawa 

 Creek crosses, and continue in a course a little W. of N. for many 

 miles. In a southerly direction they are found near Queanbeyan, to 

 the east of the Yass-Canberra Federal City area. The width of this 

 belt of country is variable, but in the vicinity of Yass it is about six 

 miles. 



Intrusions of porphyry are to be found at irregular intervals 

 all along the line of strike, and the weathering of this porphyry into 

 a good soil makes farming on a small scale possible in certain 

 localities. 



Numerous veins of milky quartz are very common in these 

 shales, and not being so readily decomposed as the shale, large areas 

 are covered with the angular white fragments. Some of the hiUs in 

 this region have their cores formed of this quartz, the •' Needles " 

 (2,533ft.) being one of them. At the summit of this hill a shaft 

 was sunk some years ago by prospectors for gold, but was abandoned 

 nothing of a payable nature being found. Similar results have been 

 obtained all along this Jerrawa belt. 



No. 1 Porphyry. — The Jerrawa shales are bounded on the west 

 by a quartz-porphyry, which I call No. 1, and as mentioned before 

 appears near the 181^ mile railway peg The strike of this porphyry 

 is about 20° W. of N., and Mt. Hawkins (2,588 ft.) is composed of it. 

 This intrusive mass or flow should have careful scrutiny, as in many 

 places it has the appearance of a clastic rock. In the railway cutting 

 near the 183 mile peg it is brecciated and fossiliferous, containing as 

 it does granitic and felsitic lumps mixed with shale, limestone and 

 fossils, such as shell fragments, crinoid ossicles and corals Cyathop- 

 phyllum and Favosites. The binding material or matrix is porphy- 

 ritic, and tlie whole mass is very compact and hard. Some portions, 

 probably limestone and fossils, have been replaced by iron pyrites, 

 the weathering of which has caused deep brown stains. This re- 

 markable bed is either a tuff bed or an example of the Silurian sedi- 

 ments being intruded and partly digested by a mass of quartz 

 porphjn-y. Mr. L. F. Harper has already dealt with a similar 

 occurrence at Boambola, near Yass.^ 



A large massive outcrop of this fossiliferous porphjnry is to be 

 seen on the hill a few chains to the north of this spot. In 



1 Harper, L. F. : Records Geo. Surv. N.S.W., Vol. IX., Pt. I., 1909. 



