250 H. I. JENSEN. 



Cretaceous. Subsequently Mr. R. Oambage, f.l.s., dis- 

 covered another area of gravels and boulders, similar to 

 and correlative with those of Glenbrook, on the heights to 

 the west of Mulgoa overlooking 4 The Basin ' where the 

 Nepean and Warragamba rivers unite. These gravels as 

 well as those of Glenbrook have been recorded on the 

 ' Geological Map of the Country in the Vicinity of Sydney' 

 under the direction of Mr. E. F. Pittman. As far as the 

 writer is aware no reference has ever been made to the 

 series of river gravels which are the subject of this note. 



On a visit to the Penrith and Windsor districts last year 

 Mr. 0. Wilson, Engineer of the Public Works Department, 

 drew the writer's attention to the existence of gravels and 

 boulder beds following a direct line between Richmond and 

 Windsor and having their maximum development near 

 Rickaby's Creek. The gravel areas were carefully mapped 

 by Mr. O. K. Hutchison, Surveyor of the Works Depart- 

 ment, in the course of the preparation of a soil map of the 

 district. The accompanying map, figure 1, copied from 

 the official soil map by permission of the Works Department, 

 shows the position of these outcrops, which the writer 

 personally inspected and examined on several visits to the 

 district. 



The boulders range from a few inches to over a foot in 

 diameter, and are composed of the same kinds of rock as 

 the Glenbrook gravels, namely granite, quartz-porphyry, 

 quartzite and slate. The sandy matrix is in many places 

 compacted into a fairly coherent rock, and in one place, 

 about three miles south of Penrith, it had been silicified by 

 spring action, so that the cement was harder than the 

 included boulders. 



The boulder beds usually form ridges, and the outcrop 

 generally has a width of from 200 to 400 yards, while the 

 depth of the gravel must in many places exceed 30 or 40 



