144 president's address — section c. 



portion of the auriferous belt of the Murchison, and described a series 

 of fine-grained volcanic ashes — lying almost horizontally on the granite 

 of Mount Yagahong — about two miles south of the town site of Gaba- 

 nintha. The beds have evidently a wide extent in the Murchison. 

 At the town of Cue, some distance to the south of Gabanintha, there 

 is a horizontal dolerite sheet capping what is known as Cue Hill, and 

 some little distance to the west, on the lower ground, are a few outliers 

 of quartzite on a lower horizon. These quartzites evidently form part 

 of a much more extensive formation — of which there are but remnants 

 left. There is very little doubt that these beds form part of the same 

 series as the volcanic ashes at Gabanintha. 



The igneous rocks associated with the series in the type district 

 consist generally of acidic lavas. The great mass of the rocks consists 

 of separate lava flows, each of no great thickness ; some of the lavas 

 are distinctly amygdaloidal, the cavities being filled with chalcedony. 

 Some of the finer-grained ashy beds differ very little in general 

 appearance from many of the banded lavas with which they are 

 associated. 



Undoubted volcanic jocii, from which these lavas emanated, 

 occur in many parts of the district, though they have been extinct 

 long enough to allow the process of weathering to reduce them to mere 

 stumps. There are also several acidic dykes which pierce both the 

 sedimentary and the volcanic rocks, and these, in all probability, 

 represent but another phase of that extraordinary volcanic activity 

 which occiirred in the northern portion of Western Australia during the 

 Devonian period. 



Considerable interest attaches to the Nullagine series by reason 

 of the nature of the boulder beds at this base of the formation, for two 

 important scientific reasons, viz. : — (a) The occurrence of flattened 

 and striated pebbles to which a glacial origin has been assigned, and 

 (6) the nature of the gold and iron ore in the conglomerate. 



The basal conglomerate of the series is made up of rounded, 

 ellipsoidal, or subangular fragments of the older underlying series. 

 Many of these often include pieces which reach a length of 3ft. or 4ft. 

 Some portions of the conglomerate contain flattened and striated 

 pebbles of fine-grained sandstone and sandy shales, identical in charac- 

 ter with those constituting the underlying strata. To these striated 

 pebbles a glacial origin has been assigned by the late Mr. S. J. Becher, 

 and subsequently by Professor David. .The pebbles, however, seem 

 to have had their striation induced prior to their taking part in the 

 formation of the Nullagine series. The beds upon which the series 

 rest, and to the denudation of which the boulders owe their origin, 

 having, as has already been shown, been subject to intense mechanical 

 deformation, it would only be natural to find some slicken-sided frag- 

 ments and pebbles in newer rocks. Earth movements have caused 

 the Nullagine beds to be thrown into a series of undulatory folds, but 

 the deformation thus induced has not been of sufficient intensity to 

 cause any striation of the component pebbles. 



