BY -W. K. BENSOK, ■«•. S. DVS, AXD W. R. BROWXE. 315 



beeu by a siuglf cycle of movement aud erosion, Ijut by a series of movements, 

 regiojal and locals the effects of which would alone suffice to give much com- 

 plexity to the present drainage system even if it were not for the complicating 

 factor of the very variable hardness of the structures on to which they were super- 

 imposed. In the regions of harder structures some indications of the former 

 valley system may still be preserved, but in the softest mudstones the streams have 

 now succeeded in obliterating nearly all trace of their complex history, producing 

 the apparently simple, and approximately consequent drainage of the Tamworth 

 Plains. 



Summary or Geological History. 



The long-continued subsidence and sedimentation of Devonian times was con- 

 tinued into the Carboniferous Period, and an invasion of a marine fauna with 

 strong aflBnities with that of Western Europe took place about the middle of 

 Lower Carboniferous times. Volcanic eruptions occurred from time to time, 

 producing intercalated layers of tuff, and occasional bands of conglomerate may 

 indicate some crust movement. The presence of Lepidodendron leUheimiaiium in 

 place of the L. oust rale of Devonian times indicates a change in the flora of ad- 

 jacent lands. 



Crustal upwarping became more pronounced, and explosive volcanic activity 

 gi-eatly increased. Hydrothermal siliceous solutions affected some of the flora 

 (gymuosperms and some indeterminable roots) and an overwhelming predominant 

 deposition of keratophyric tuff took place, intercalated with conglomerate bands, 

 a little mudstone, and rarely flows of basalt. Glaciers formed on the adjacent 

 uplands, and discharged great masses of fluvio-giacial conglomerate and till, and 

 locally there appeared widespread lakes in which the water, charged with rock 

 flour, deposited seasonally banded "varve" sediments, which became contorted 

 through subsequent thrusting from stranding ice-floes, the presence of which float- 

 ing in the lakes, is indicated by the occurrence of large boulders drop]3cd among 

 the banded clays. The plants of the period were now Ehacopteris and Calamites. 

 Meantime explosive eruption continued with varying intensity, felspathic material, 

 but occasionally rhyolitic, being produced, and this was interstratified with con- 

 glomerate, etc. Perhaps some ba.sie flows occurred. There followed, however, 

 possibly after a hiatus, a huge development of flows of basalt derived from fis- 

 sures, and perhaps at the same time a great development of sills of intermediate 

 and basic rocks in the sediments beneath the basalts. Crust warping, fracturing, 

 and extensive differential movement (block-faulting) followed, and with or after it 

 a great development of keratophyi-e and quartz keratophyre sills and dykes radi- 

 ating from the volcanic centre of Warragiuidi. Here, too, many dykes, sheets 

 and sills were formed in the basalts about the volcanic centre, where several large 

 masses of breccia now filled the volcanic vents. Dykes of basalt and dolerite, ex- 

 tending into the older formations, formed aljout this time also. This great eruptive 

 activity concluded the Carboniferous or ushered in the Permo-Carboniferous 

 Period. 



Long continued erosion followed, but at tlie close of this latter period, the 

 region had become one of deposition of the Newcastle Series of Glossopteris- 

 bearing sandstone. The final movements of the epoch of crustal instability which 

 appeared in Carboniferous times, broke up the Permo-Carboniferous. or Permian 

 sediments, and let down small blocks into the general platform of older structure, 

 where they have been preserved from erosion. The jfesozoie Era closed with the 



