120 PROCEEDINGS OF THE ROYAL SOCIETY OF QUEENSLAND. 
appreciated by comparing analyses representative of the 
rocks of the two areas. The analyses used for the Southern 
Coalfield area are those quoted by Harper on page 284 of 
his memoir. These are eight in number. It will be noticed 
that the highest silica percentage in Harper’s analyses is 
59-64, while the majority of the flows in the Silverwood area 
are rhyolitic, and a typical analysis gives 73-93 percentage 
of silica. However, there is what in the hight of modern 
petrogenesis must be considered an even more important 
chemical difference than the divergence in the average 
silica percentages, and that is the amount and proportion 
of the alkalies and lime present. In order to fairly 
illustrate this difference, the three analyses from the Silver- 
wood-Lucky Valley volcanics which bear the closest 
resemblance in silica content to the Southern Coalfield rocks 
are compared with the eight available analyses from the 
latter area. 
Extreme Values of | 7 r 
Oxides of three | @xtteme Values of 
=a Oxides of eight 
—_— Analyses from 
Silverwood—Lueky Analyses from 
ze *~ | Southern Coalfield, 
Valley. 
SiO, = ee Shay) SE Daas 51-07 —59.64 
ALO, 9 TOS ETN Lae OIE ie ere 15-18 —18-82 
FO, 4. eit eee 1-72— 3-16 2-45— 7-30 
FeO ray Sts a de 427— 6-65 2:97— 5-40 
MgO ee ee by tre Oh 2-75— 5-10 1-66— 4-09 
CaO ne) ie oe aE 581— 8-15 | 388— 7-72 
Naloien dct sa eee 230— 4-11 3-10— 3-97 
K,O Ay ce ane Se O-11— 0-62 2-75 — 5-88 
HOS pact) Lad ices 1-03— 2-19 1-07— 2-89 
TiO, pT aT Peewee 1-70— 1-82 |  0-42— 1-20 
P.O, eh 0-14— 0-21 | 0:34— 0-88 
The most striking difference in the two series 1s seen in 
the values for K,O. The large amount of this oxide in the 
Southern Coalfield gives rise to the curious orthoclase- 
basalts and allied types in that area, which are in marked 
contrast with the volcanics with which we are concerned. 
(ce) The Drake Area.—The Drake area is of interest in 
the present connection for several reasons. It is the closest 
area which contains late Palwozoic volcanics comparable 
with those of the Silverwood-Lucky Valley district, being 
enly some 50 miles distant. Lithologically the rocks of the 
