194 GEOLOGY AND PETROGRAPHY OF CLAEENCETOWN-PATEESON DISTRICT, i., 



tributary of Dunn's Creek. The varves outcropping within the village of Sea- 

 ham, and excellently described by Sussmileh, may be followed from the main road 

 some distance to the west, the lower and more important horizon being the more 

 persistent. ' 



On the northern side of the Williams River, in the region mapped, the Main 

 Glacial Beds do not form important outcrops, much of the area where one should 

 expect to find them being occupied by swamps and alluvium. However, they 

 occur in a band about 30 chains wide, from the Punt Crossing to Caswell's 

 Creek, the representative of the series being conglomerate, the ^appearance of 

 which suggests a fluvio-glacial origin, although no striated pebbles have been 

 found. 



IisTTEUsrvE Igneous Rocks. 



The eruptive rocks which are definitely intrusive form a very subordinate 

 group, occurring as sills and dykes. Three distinct types are comprised in this 

 group. 



Firstly, there is a dyke of quaxtz-bearing gabbro-porphyrite, occurring in 

 portion 114, Parish of Barford. It forms a small knoll just to the east of Mr. 

 Vogele's cottage, and can be traced about half a mile to the north and half that 

 distance to the south. The dyke strikes N. 10° E. and has an inconstant width, 

 varying from 10 to 30 feet, but no particulars could be obtained as to the dip. 

 On the margins of the outcrop the rock is distinctly fine-gTained. The main 

 mass is a grey rock of very compact nature, weathering spheroidally, and giving 

 surfaces which it is almost impossible to spawl. The rock is porphyritic in plagio- 

 clase in hand-specimen, and under the microscope one sees large labradorite 

 crystals set in aij ophitic groundmass of medium gTain-size, composed of augite, 

 ilmenite, plagioclase arid interstitial quai-tz. 



Secondly, we consider a group of intrusions in the railway cutting in por- 

 tion 2, Parish of Wallarobba, just south-west of the Station. Here there is a 

 sill and three dykes of basic material intruding the hornblende-andesite (Martin's 

 Ck. type). Two of the dykes are about one foot in thickness, and the third eight 

 inches, while the sill has a width of 10 feet. Unfortunately the rocks are almost 

 completely decomposed, but there is no doubt of the material being basic and 

 originally probably basaltic or doleritic. 



Thirdly, there is a dyke of felsite intruding Burindi Beds' in a railway 

 cutting between Martin's Ck. and Hilldale, just north of the 40 mile-peg, which 

 strikes N. 50° E. and has a width of 4 feet. The microscopic characters of this 

 rock are not yet known. 



The question arises as to the ag'e of these minor intrusions. The felsite is 

 post-Burindi and might reasonably be regarded as connected with the eruption of 

 the felsitie lavas of the Volcanic Stage of the Kuttung Series, and all that can 

 be said of the quartz-bearing gabbro-porphyrite and the basic rocks is that they 

 are post-Volcanic Stage. They are essentially similar to the material forming 

 some of the minor intrusions of Tertiary age in Eastern New South Wales, and 

 in view of the occurrence of Cainozoic basalt flows at Mt. Douglas and elsewhere 

 in the area, the possibility of the large dyke of quartz-gabbro-porphyrite having 

 been a feeder to the basalt sheets produced by fissure eruptions, must be recog- 

 nised. However, it is also to be pointed out that at Currabubula there are rocks 

 of the nature of quartz-dolerites among the Carboniferous rocks, and also at 

 Pbkolbin some small occurrences of dolerite and basalt, possibly of Palaeozoic 

 age. 



