298 PROCEEDINGS OP SECTION C. 



of limestones, black and grey pyritous shales, sandstones, grey- 

 wackes, grits, and conglomerates, interbedded with tliese are 

 rocks of volcanic origin, some of the above having undergone 

 considerable alteration. In all, there are about 2,020 feet in 

 thickness of the auriferous strata, which lie with great regularity 

 dipping to the east. 



A large number of fossils have been collected from these beds 

 by Mr. Jack and myself, which were sent to Mr. Robert Etheridge, 

 Junr,, for examination, who pronounced them to be homotoxia 

 with the Carbonifero-Permian. 



There are four distinct zones of black shale, or " slate " as it 

 is locally termed, and the reefs, as a rule, are payable only when 

 in contact with these shales. It is in the upper of these beds, 

 which is about 200 feet thick, that the boulders I'eferred to occur. 

 The bed consists of a fine black pyritous aluminous shale. 



The boulders are not very numerous, nor do they appear to 

 have been distributed generally over the field, as it is only in a 

 few mines that I have noticed them. 



I will describe two of these boulders, as instances : — One from 

 the No. 1 North Phoenix Mine, at a depth of three hundred and 

 seventy feet, consisted of a fine-grained siliceous rock — a siliceous 

 greywacke. It \\ as found about the middle of the bed, at a point 

 where the shales had, for a foot or two in thickness, passed into 

 what might be more properly called a fine aluminous sandstone. 

 The boulder was flat and smooth, its dimensions being 13 inches 

 X 10| inches x 5 inches. 



In the Phoenix Golden Pile Mine at the 700 feet level, several 

 boulders were met with in driving a cross-cut in the shale ; they 

 consisted of a coarse altered greywacke, containing ill-defined 

 crystals of felspar, and cubical and pyramidal crystals of iron 

 pyrites. The largest of these was broken in two ; the dimensions 

 of the part i^reserved were 3| inches x 5| inclies x 4^ inches, the 

 length of boulder must originally have been at least double that, 

 making it 3|^ inches x 5^ inches x Sh inclies. These were in fine 

 laminated pyritous shales. 



It is difiicult to say where these boulders have come from, or 

 how far they may have travelled, for although greywackes similar 

 to those of which they are composed are found among the rocks 

 on the field itself, tliey are also common throughout the whole 

 of the Devonian and Lower Carboniferous rocks which occupy a 

 large area in this district 



The presence of boulders of such size, in a rock which was 

 originally a fine mud or silt, would seem to indicate that glacial 

 conditions existed at the time tlie Gympic rocks were being- 

 deposited, they having been dropped from floating ground-ice ; I 



