252 H. I. JENSEN. 



feet. The height of the boulder ridges is variable, ranging 

 from 40 to perhaps 150 feet above the present water level 

 of the Nepean River. The boulder formations run slightly 

 north of north-east from the Penrith alluvial plain, at a 

 point three miles from Penrith where the present Nepean 

 River turns abruptly to the west. They are approximately 

 parallel to Rickaby's Creek. 



To the north and west of the line of gravels the soils are 

 mainly of alluvial origin, consisting of light sandy loams 

 which are partly the product of river deposition during the 

 period when the river was changing its course from the 

 line of gravels to the present bed, and partly redistributed 

 silt washed down from the old bed now represented by the 

 gravel hills. A few isolated patches have soils indicating 

 derivation from Hawkesbury sandstone and Wianamatta 

 shale. To the south and east of the line of gravels the 

 soils invariably indicate their derivation from the Wiana- 

 matta shale formation. 



The gravels along this line are far more extensive than 

 those of Glenbrook and Mulgoa. They unquestionably 

 belong to the same age and are of the same derivation. The 

 vast stretch of poor sandy soil between the old gravels and 

 the allu vials of recent age is of drift origin as above stated, 

 and may indicate a rapid shifting of the river from its 

 ancient to its present course. The Glenbrook, Mulgoa 

 and Rickaby's Creek gravels are in the writer's opinion of 

 late Tertiary, Pliocene or Pleistocene Age. 



From a study of the country around Penrith, Mulgoa, 

 Windsor and Richmond, the writer has arrived at the con- 

 clusion that in late Tertiary times (probably Pliocene) the 

 Warragamba river flowed in the course now occupied by 

 Mulgoa Creek, the gravels on the elevations east of Penrith 

 indicating that the old Nepean often meandered east of the 

 course marked by Mulgoa Creek and the present river. 



