68 GEOLOGY OF MT. FLINDERS AND FASSIFEKN DISTRICTS. Q., 



sandstones, conglomerates and shales to which the name "Ipswich 

 Formation " has been given; and which, from the fossil plants 

 contained in it, has been referred to the Upper Trias-Jura. The 

 whole series has been greatly faulted and folded, the folding in 

 some cases being due to compression of trough-faulted blocks. 

 Here and there basalts have burst through the fissures and covered 

 considerable areas. Such is the case at Booval, near Ipswich. 

 In Ipswich proper a hill known as Limestone Hill is capped with 

 a deposit of secondary limestone and siliceous sinter. These 

 substances are leached out of a mass of decomposed basalt and 

 basaltic tuff, w4iich has been extruded from a curved fissure. In 

 other places basaltic cones of considerable height may be seen, as 

 Mt. Forbes or Walker, about 15 miles S.S.W. of Ipswich. This 

 mountain intrudes the Walloon Seiies, the newest of the Ipswich 

 Formation, and flows from Mt. Walker cap the Walloon Series 

 over considerable areas. To the west and south-west of Ipswich 

 the Coal Measures are not so faulted aud tilted as at Ipswich. 

 These Coal Measures form the Walloon Series, which is separated, 

 according to Rands and Cameron, by a probable line of fault 

 runnins: N.E.-S.W from Fernvale in the direction of the Flinders 

 Mountain group. Towards the N. W., this fault forms the border 

 between the Palaeozoic rocks of the Parishes of Burnett and Sahl"*^ 

 and the Walloon Series. The Brisbane River, although it 

 meanders into the Ipswich Formation, in places has a tendency 

 to follow this fault through some part of its course. After the 

 Brisbane River has swerved to the east, flowing north of the Pine 

 Mountain inlier, the fault continues in its original direction 

 separating Pine Mountains from the Walloon Series, and further 

 to the S. W. Deebing Creek practically flows parallel to the fault- 

 line. 



This fault is of importance in the discussion of the geology 

 of Mt. Flinders because the mountains of the Mt. Flinders group 

 lie to the east of it in the intensely faulted and crushed strip of 

 country which lines the eastern side of that fault. In this strip 



* See Cameron's map No. 2 of the Ipswich Beds. 



