6 
The Queensland Naturalist Sept., 1936. 
valleys, as was found to be the case near the camp where 
only a low divide separates the Albert waters from Widgee 
Creek which is a tributary of the Logan. 
The sedimentary rocks exposed in the valleys of the 
Upper Albert, and Widgee and Christmas Creeks belong 
to the Walloon coal measures of Jurassic age, and we say 
some outcrops of coal characteristic of the Walloon series. 
The volcanic rocks are mostly lavas and fragmentary 
materials of the dark basaltic types but light-coloured 
trachytic or rhyolitic rocks are also prominent. 
The determination of the period in which these vol- 
canic rocks were extruded has long been a controversial, 
perhaps one might say, a burning, question to geologists. 
The earlier geologists, Dr. R. L. Jack and Mr. W. H. 
Rands thought all the volcanic rocks belonged to the then 
termed Trias- Jura period, that is, that they were more or 
less contemporaneous with the sediments now classed as 
Jurassic. Dr. H. I. Jensen considered that they were all 
of much later age — Tertiary. In 1909 the writer of these 
notes, after working between Brisbane and Beaudesert, 
was inclined to a contemporary age for some, but not for 
all of the volcanic rocks encountered, but had not found 
any unequivocal evidence. Certain basalts near Brisbane 
and Ipswich had then long been accepted as definitely 
proved of Tertiary age. A flying, or rather a hurried 
equestrian visit to Christmas Creek, with a hurried 
before-breakfast examination of a certain outcrop shown 
to him by Mr. Buchanan, seemed to show quite definite 
evidence that some of the volcanic material was contem- 
porary with the coal measures. A vertically tilted shale 
arid sandstone had, so he recorded, rounded fragments of 
volcanic rock included in the sandstone. 
Mr. R. A. Wearne, in another area, and for other 
reasons at about this time came to the same view that part 
of the volcanic rocks were of Walloon age, 
In 1916 Professor H. C. Richards took up the study of 
and came to the conclusion that all the volcanic rocks were 
later than the Walloon, regarding them all as of Tertiary 
age. He especially visited the section on Christmas Creek, 
and described the vertical sediments as being a mass of 
shale many feet in diameter, included in a volcanic agglo- 
merate. The shale contained characteristic mesozoic fos- 
sils, and the section demonstrated clearly to him that the 
agglomerate was of later age than enclosed shale. He did 
not refer to having observed any sandstone in the section, 
but on the other hand mentions that it was remarkable 
that the previous observer should have regarded the vol- 
canic material as sandstone. 
