742 PERMIAN AND TRIASSIC INSECTS FROM N.S.W., 



Section B. The Triassic Insects. 



Mr. Mitchell's Collection contains twenty-five specimens from 

 the Wianamatta Shale Beds. Of these, No. 10 is from Narellan, 

 about five miles from Campbelltown, along the branch line from 

 this latter town to Camden. The horizon of this specimen is 

 probably about 700 feet above the top of the Hawkesbury Sand- 

 stone. The rest of the specimens, numbered 1-9, 11-22, and 

 34-36 inclusive, were taken in the railway cutting at Glenlee, 

 some four miles south of Campbelltown, on the main Southern 

 Line. 'I'he horizon of these specimens is between 300 and 400 

 feet above the top of the Hawkesbury Sandstone. 



The succession of strata from the Hawkesbury Sandstone to 

 the Wianamatta Shales is not by any means continuous. For a 

 long period subsequent to the elevation of the former, this series 

 of rocks was subject to sub-aerial forces. Afterwards, the great 

 subsidence of the area occurred, from the Blue Mountains to 

 Bowral in the South. Into this depression, the Hawkesbury 

 River emptied itself near Mulgoa, forming the Wianamatta 

 Lake. When this lake was tilled up, the excess of water was 

 drained off through the original channel of the Hawkesbury 

 River, until this became sujQ&ciently degraded to cause the lake 

 to disappear, and its area to be denuded, as we now observe it 

 to be. Thus a length of time sufficiently long elapsed, between 

 the end of the Hawkesbury Series and the beginning of the 

 Wianamatta, to allow of the advent of many new forms of plants 

 and animals, though Tceniopteris and Thinvfeldm persisted 

 through the two series. 



As regards the age of the Wianamatta Series, I cannot do 

 better than quote Mr. Walkom. In his last letter to me he 

 writes, "On the evidence available, the Ipswich flora indicates 

 distinctly an Upper Triassic age, possibly Rhsetic, but more pro- 

 bably older (Keuper); also, the Wianamatta is probably of the 

 same age." In the concluding portion of his work on the Flora 

 of the Ipswich and Walloon Series,* which has just been pub- 



* Mesozoic Floras of Queensland. Parti., concluded. The Flora of 

 the Ipswich and Walloon Series. [d) Ginkgoales, (e) Cycadophyta, (/) 

 Coniferales. By A. B. Walkom, B.Sc. Queensland Geological Survey, 

 Publication No.'ioO. Biisbane, 1917. 



