Probable Miocene Age of Conglomerate, Shelford. 181 



at about forty feet from the top of the bank, and continues for 

 thirty-five feet lower down the hill, it follows that the estuary 

 or inlet was invaded by the niiocene sea until about one-third 

 of the present depth of the gorge had been excavated. The 

 conglomerate for the whole of the thirty-five feet of vertical 

 extent in which it is traceable is intermingled with blocks of 

 lava, and is therefore probably nothing more than a collection 

 of scattered boulders resting on the basalt and not reaching far 

 below the surface. The iron oxide in them is of course derived 

 from the basalt, while the quartz pebbles plentifully intermixed 

 with it were doubtless washed down from silurian country higher 

 up the river. 



The southern portion of the Leigh River has not been geologi- 

 cally surveyed, but in a report upon its upper course by Messrs. 

 Etheridge and Murray, written in 18.68, but not published till 

 1874,* it is incidentally remarked that the basalt around Shelford 

 was derived from Mount Mercer, an extinct crater seventeen 

 miles to the north. In describing the results of their detailed 

 work, which was confined to the more northern area mentioned, 

 the further statement is made that certain drifts and gravels, 

 classed by them as pliocene underlie the same basalt. Such a 

 position for pliocene strata is manifestly opposed to our theory 

 that the igneous rock is not younger than miocene. It is possible 

 that the basalt they refer to may belong to a different flow, more 

 than one being mentioned in their report, but as we did not visit 

 the sections in the surveyed area, we can offer no opinion upon 

 the point. We may remark, however, that the geological ages 

 of the various drifts and gravels of Victoria are not precisely 

 known, the descriptive terms applied to them by the geological 

 survey being admittedly, to some extent provisional. The best 

 of all evidence is, of course, that afforded by marine fossils, but 

 from the nature of the case, it is seldom available. Moreover, 

 the revised nomenclature of the tertiaries adopted by the 

 majority of recent writers has to be considered — if, as they 

 contend, the former miocene of the survey has to be read as 

 eocene, possibly also the term pliocene may, in some cases at 

 least, need to be interpreted as miocene. 



* Progress Report, No. II., p. 101, et seq. 



