ohapteh XXV. 
THE TRIAS-JTJRA SYSTEM— 
THE IPSWICH EORMATIOH (UPPER TEIAS-JUEA), IK THE TYPE DISTRICT. 
An area of about twelve thousand square miles in the south-eastern corner of 
Queensland is occupied by the Ipswich Coal Field. Its strata consist for the most pait 
of fine conglomerates, grits, white, grey, and brown sandstones and shales, Avith a numbei 
of coal-seams and beds of fireclay. 
At or near the base of the formation, as seen in the neighbourhood of Brisbane, 
is a rock consisting of a felsqjathic matris, with blebs of quartz and some crystals of 
orthoclase felspar, and containing pebbles of micaceous schist and quartz, which, toAvards 
its base, attain the size of boulders. It is generally Avhite or yellondsh-white in colour, 
although in places it has green, purple, or brown tints. Near its base it contains pieces 
of silicified and carbonised wood. This rock, Avhich is easily Avorked, yet tough and 
durable, has been eninloyed over since the founding of the City as a building stone, 
-although in modern buildings it is now, to a great extent, superseded by the sandstones 
of Murphy’s Crock, &c., Avhich also belong to the IpsAvich Formation. It is obviously a 
clastic rock, although felspar crystals and quartz blebs have been developed in it subse- 
quent to its deposition. It has a rude sort of stratification, and its true nature can best 
be obserA^ed on weathered surfaces. It was formerly classed as a porphyiy, and regarded 
as being intrusive through the schists, &c., which crop out in adjoining portions of the 
City ; but there can be little doubt that it is in reality a volcanic ash. o • 
In the road cutting in Ann Street the ash or ashy sandstone dips at 18°, and is 
separated by thirty one inches of light and dark-coloured shales from the older micaceous 
schists on which the shales lie unconformably. Near the Children’s Hospital, a con- 
glomerate intervenes between the ash and the schists.* 
In the immediate neighbourhood of Brisbane the Ipswich Formation has not yet 
furnished any coal-seams of great importance. In a Avell at Kedron Lodge the strata 
observed betAveen the depths of twenty five and forty feet were alternate layers of coal 
and fireclay, the former never over one foot in thickness. Small coal-seams have been 
met Avith in shafts at Ballinger’s, about three miles north of Kedron Brook. 
In a bore in search of artesian water at the Racecourse, or “ Eagle Farm, in 
1889, “down to a depth of si.v hundred and fifty feet, the strata passed through were 
blue and grey sandstones, and shales in alternate layers. Ih-om six hundred and fifty 
feet to six hundred and seventy feet a bed of carbonaceous shale, with layers of sand- 
stone, and three seams of coal, was passed through. From six hundred and seventy 
feet shale and sandstone, with layers of coarse gravel, were pierced, till at a depth ot 
seven hundred and ninety feet, a seam of good coal was met with, which, so far as could 
be judged by the nature of the drilling and the sludge brought up in the pumps, has a 
thickness of five or six feet. Below this seam a carbonaceous shale, sandstone, and 
thinner scams of coal, from six inches to three feet in thickness, have been passed 
through, down to the depith of eight hundred and seventy five feet, t 
* Report to accompany Geological Map of the City of Brisbane and its Environ.s. By W. H. Bands. 
^^risbane : by Authority: 1887. i q.v, t i sesQ 
+ Report of Mr. William McKinnon, Overseer to the Hydraulic Engineer, 18th dune, ibsa. 
