BY G. D. OSBORNE. 169 



dal phases are similar to those found at Martin's Creek, descriptions of which 

 are given below. The pitehstone is of a general black body-colour with a num- 

 ber of red veins of iron-stained material, possesses a resinous lustre and, under 

 the microscope, shows phenoorysts of andesine and hornblende set in a glassy 

 base which contains a number of microlites, and patches which have been pro- 

 duced by devitrification. 



In portions 99 and 141, Parish of Barford, near Tumbledown Creek, one 

 finds tkree varieties of hornblende-andesite. The first is the glassy phase found 

 at Wallarobba, and this, being not more than 20 feet thick, is followed by a 

 thin band of a daxk gTeenish-black z-ock possessing a greasy lustre and uneven 

 fracture. This contains phenocrysts of biotite, hornblende, hypersthene, augite, 

 and occasionally plagioclase set in a glassy base. It is succeeded by 50 feet of 

 the normal lithoidal hornblende-andesite. 



At Martin's Creek three large quarries have been opened in the hornblende- 

 andesite, which has here its maximum development for the region under con- 

 sideration. The writer had the opportunity of visiting all the quarries, and 

 was able to study in detail the property of The State Metal Quarries, Ltd., where 

 there occur at least four distinct phases of hornblende-andesite. These are (i.) 

 a pale blue rock with phenocrysts of plagioclase and subordinate hornblende, 

 (ii.) a lighter coloured rock, hornblende dominating over plagioclase, (iii.) a 

 deep blue rock with equal amounts of hornblende and plagioclase as phenocrysts, 

 and (iv.) a felspathic rock with very little hornblende. 



The Mt. Gilmore Section. (A-B on Map). Text-fig. 1. 



The maximum thickness of the rocks of the Volcanic Stage is found in the Mt. 

 Gilmore ai-ea. A detailed section is to be obtained along the line A-B, as follows: 



Starting with the base of the hornblende-andesite exposed on the left bank 

 of the Williams River opposite Clarencetown and going south-east over the dip- 

 slope of andesite, one passes on to tuffs containing sporadic pebbles up to one 

 foot in diameter. These tuffs give poor outcrops, but some of the few exposures 

 exhibit current bedding. Above these is the hypersthene-andesitic pitehstone, 

 the rock being for the most part decomposed. Here and there small shatter 

 zones occur in which cementation of the fragments of pitehstone has occurred, 

 the nature of the binding material being indeterminate on account of the 

 weathered state of the whole. Above the pitehstone are tuffs and conglomerate 

 similar to those below it, and these end under a thin band of sodi-potassic 

 rhyolite which has an abundance of biotite, imparting to the rock a spangled 

 appearance. Above this is a conglomerate formed of well-corroded pebbles, with 

 an intercalation of fine red tuff. This is succeeded by an important flow of 

 biotite-quartz-keratophyre, which is developed to a greater extent a little to the 

 south on the right bank of the river. The line of section is now continued from 

 this point, where there are two flows of keratophyre separated by 25 feet of 

 conglomerate. Particularly good opportunity of examining fresh material is 

 afforded by the quarry which is opened upon the larger of the flows, and the 

 rock is seen to be more or less homogeneous, of a blue colour, and possessing 

 an abundance of quartz, biotite and plagioclase felspar. On the surface of the 

 smaller flow there lies a thick mass of conglomerate and tuff which is succeeded 

 by a lava of the nature of a type transitional between soda-rhyolite and dacite. 

 This rock is distinctly spherulitio and may be obtained in a very fresh state. It 

 is overlain by conglomerate, in which there is an intercalated band of quartz 

 keratophyric tuff, containing angular fragments of quartz and clear albite, to- 

 gether with inclusions of glassy rocks and patches of secondary silica. Follow- 



