370 T. W. E. DAVID. 



ing sufficiently rapid to produce a lake on the downthrow 

 side in either the Grose or Oolo Valleys ? if so, traces may 

 be found of such lacustrine beds. On the contrary, the 

 faulting may have been so slow that the Grose and Oolo 

 Rivers may have been able to deepen their channels on the 

 upthrow side of the fault at a rate sufficiently rapid to 

 keep pace with the subsidence on the downthrow side. 



Age. — As regards age it is clear from the large amount 

 of denudation which the upthrow side of the fault plane 

 has undergone at Kurrajoog Heights (see left of Plate 17) 

 that tlie fault cannot be very modern. Since the faulting 

 occurred a large wedge-shaped slice has been worn off the 

 upthrow side of the fault, and this measures in places 500 

 feet thick, about 14 chains wide, and about 20 miles long. 

 The above, it may be added, is a low estimate of the amount 

 of denudation subsequent to the faulting, as the Wiana- 

 matta Shales at the time of the faulting probably had a 

 thickness of at least 100 feet, whereas in the above estimate 

 a thickness of only 20 feet has been assumed for them. 



In conclusion I beg to thank Mr. Halligan for his kind- 

 ness in surveying the present slopes near the fault plane, 

 and Messrs. G. E. Oollett and W. G. Woolnough, b.sc, f.g.s. 

 for assisting in the work. The Road Superintendent, Mr. 

 Norman Grant, gave useful assistance by placing the ser- 

 vices of his foreman at our disposal. Mr. E. P. Pittman 

 kindly examined all the sections in the field with me, and 

 joined with me in the collecting of evidence for drawing 

 Plate 16, and I am much indebted to him for his help and 

 criticism. Mr. G. W. Card, was good enough to assist me 

 with his aneroid observations ; and I desire to thank my 

 colleague, Mr. W. S. Dun, f.l.s., for kindly supplying biblio- 

 graphical references. 



