122 ^ ^f .lOIl^CSTON >ri:MORIAL LECTUKE. 



6ft Oin. Dark grey fine sandy silt, compact and 

 dark grey, through peaty material. 

 This rests on a slightly eroded sur- 

 face. 

 4fl Oin. Gritty, pebbly sand rock; the aboriginal 

 chalcedonic flake occurred in this 

 layer, immediately overlying the 

 stream tin gravel below. 

 8ft. to 12ft. Oin. Gravelly consolidated drift, with 

 in places thin- stream tin and well rolled pebbles 



ning to 3ft. of quartz and slate from 1 inch to 



3 inches in diameter, and sub-angular 

 reef quartz up to 6 inches in dia- 

 meter; pot-holes of shingle occur in 

 places about 3 feet in depth. The 

 lower pai't of this drift yields stream 

 tin at the rate of from 1 to IJlb. per 

 cubic yard. 

 Floor under stream-tin drift fine-grain- 

 ed, greenish felspathic quartzite; dips 

 W. 18 deg. S. at 18 deg. The 

 age of these sedimentary rocks is 

 .assumed to be Cambro-Silurian. 



The undulating, but on the whole flattish, floor, on which 

 the drift reposes, is just about G5 feet above the Ringarooma 

 River and 85 feet above sea-level. 



At the time these wide-spread gravels and sands were 

 being deposited, the Ringarooma River could not have occu- 

 pied tts present channel, which is about a quarter of a mile 

 to the south, and which has subsequently been deepened in 

 hard rock (partly felspathic quartzite, partly of granite) 

 by about 65 feet. At the rate of erosion determined by C. 

 C. Brittlebank for the Bacchus Marsh district of Victoria, 

 such a work of erosion might have been done by a river 

 like the Ringarooma in a period of time of the order of 

 100,000 years. 



This would surely be older than the Wiinn glaciation, 

 and would more nearly correspond with that of the Riss. 



If, therefore, this flake was really in situ, as seems orac- 

 tically certain, it would put back the coming of man into 

 Tasmania into perhaps the time of the Riss glaciation. 

 At the same time, if the early part of the Wiirm glacia- 

 tion dates back, as some think, to 50,000 years ago, the 

 excavation of the present Ringarooma valley out of the 



