202 Rev. W. B. Clarke on 



the author as running through igneous and metamorphic 

 rocks, which are laid bare over a considerable area between 

 the Cockburndoon, the Derra, and the Uringalla rivers, 

 where recent volcanic outbursts have disturbed the older 

 rocks. The sedimentary rocks wrap round the margin of 

 this area,' the beds dipping at a considerable angle. 



On the north banks of the river, at a place called Jaora- 

 min, beds of conglomerate are described, containing frag- 

 ments apparently of transition rock ; and the author consi- 

 ders, from the condition and appearance of the river banks, 

 and the fact that a wide space, at a considerable height 

 above the water, is covered with the debris of these conglo- 

 merates, that a considerable change of level has taken place 

 in the district, producing elevation. 



Having given a general account of the district, the author 

 then proceeds to describe the different plutonic rocks found 

 in it, andi states, that they consist of syenite, syenitic gra- 

 nite, protogene, and porphyritic rocks of various kinds, and 

 of greenstone, basalt, and trachyte, — all, with the excep- 

 tion of the three latter, passing, by regular gradations, from 

 one to another. The syenites are said to resemble those of 

 Skiddaw, and the syenitic granite that of Guernsey ; while 

 a protogene is described greatly resembling a beautiful rock 

 of the same kind in St John's Vale, near Keswick. 



At Arthursleigh, the author describes a spot where the 

 face of an exposed cliff exhibits a net-work of quartz veins, 

 with dykes of syenitic rock and hornstone ; and not far off, a 

 dyke of ironstone, and others of basaltic rocks, amongst 

 which are some injected trachytes, that have been used for 

 building purposes. 



Having described the position and mineral character of 

 these igneous rocks, as they appear en masse^ the author then 

 proceeds to allude to some singular instances of intrusive 

 dykes of limestone and marble, at a spot known as " Camp- 

 bells,"" or " Shepherds," situated on the estate of Arthursleigh, 

 just alluded to. Th<?se dykes occur in contact with hard, 

 large-grained, grey syenite, and were seen on the right bank 

 of the river Wollondilly. 



In the first instance mentioned, tlie width of the dyke is. 



