464 H. S. JEVONS, H. I. JENSEN, T. G. TAYLOR AND C. A. SUSSMILCH. 



to the Prospect Creek. The striking conformity of the 

 modern ground surface to the upper surface of the eruptive 

 rock is probably due to hardening of the shales. 



A study of the drainage of the neighbourhood of Prospect 

 Hill has convinced us that the intrusion reversed the slope 

 of the creek now flowing through it. The latter finds its 

 way northwards into the Parramatta River, whilst the 

 larger creek to the S. W. of the mass, named Prospect Creek, 

 flows into the George's River. Inspection of the map 

 (Plate XXXIV) shows that Prospect Hill encroaches on 

 the basin of the Prospect Creek right up to the banks of 

 that stream itself. It is probable that originally the 

 northern watershed of this basin in this neighbourhood lay 

 just south of the main Western Road, and that a creek 

 flowed from somewhere near here southwards, more or less 

 along the floor of the present valley, but somewhere to 

 the east of the existing creek, over the line where the inlier 

 of shale now reaches its lowest level. The old creek must 

 have crossed Booth's Quarry towards its east end ; and it 

 may not be extravagant to regard the well-marked gully 

 which runs S.S.E. from this quarry as an actual remnant 

 of the creek. At least 500 or 600 feet depth of shale 

 must have been removed since the reversal of the drainage,. 

 as will be explained in a later section, but there is no 

 reason to suppose that denudation need involve any lateral 

 shifting of stream beds where we are not dealing with strike 

 streams. The whole theory of superimposed drainage a& 

 usually stated, involves the assumption of comparatively 

 little lateral shifting over long ages. The watershed of 

 the valley to the east of Prospect Hill has probably also 

 been shifted a mile or so southwards. 



The reversal of drainage is no argument for or against 

 either Prof. David's or our own hypothesis. The former 

 applies whether there were an overlying valley or not; the 



