Page:Quarterly Journal of the Geological Society of London, vol. 28.djvu/349

 or old river- course. Though of course this is an error soon discovered, I have been informed that they have often found gold under such

Fig. 13. — Limestone Barrier, Broken River, Northern Queensland.

conditions ; if so, it would be a very valuable addition to our knowledge of the earliest period at which auriferous quartz veins were formed.

On the track from the Broken River to the Gilbert Diggings, Devonian rocks several thousand feet thick may be observed, as they are continuous in dip, without being repeated, for at least five miles across the strike, with an average inclination of 60°.

Although on the Broken River and its tributaries a breadth of thirty miles, with a length of sixty miles, is occupied by a persistent outcrop of Devonian strata, gold has only been discovered in remunerative quantities in a small gully, heading from a leading ridge, where a trap dyke has penetrated the Palaeozoic rocks of the district.

The following districts, however, where Devonian rocks prevail, have been centres of gold-mining enterprise : —

Lucky Valley. Talgai. Gympie. Calliope. Boyne. Morinish. Rosewood. Mount Wyatt. Broken River. Portion of Gilbert.

In every case here cited the country is traversed by trap-rocks of a peculiar character, either diorite, diabase, or porphyrite ; and tufaceous representatives of these are also found interstratified in the