I 



BY (3. D. OSBORNE. 525 



between Raymond Terrace and Seaham, says: "It is assumed that these strata 

 have split along' the axis of the anticline, and have been heavily faulted towards 

 the west, this line of the fault determining in this part of its course the trend 

 of the Williams River." 



Thus Fu, which is a strike-fault along the eastern fall of the Gilmore ridge, 

 becomes a dip-fault further to the south, on account of the plunging nature of 

 the Williams River anticline. Mr. C. A. Sussmileh has informed the writer, in 

 conversation, that as a result of observations upon the Kuttung rocks between 

 Seaham and Raymond Terrace, east of the Williams River, he has been able to 

 confirm the opinion of Professor David, and to obtain some details of the faulting. 



There still remains something to be said of the east and west fault, Fe, near 

 Hilldale and the other small dislocations. Fc cuts right across the line of section 

 X Y Z and shows at that point a stratigi'aphical displacement of 500 feet. The 

 average throw of the fault is approximately the same. It can be defined by 

 observing the extent of the marine (Burindi) rocks. This fault, throwing to the 

 north and with some transverse movement, has displaced the core of the Hilldale 

 Dome in the Burindi Series some distance to the west. 



A small fault in the Gilmore ridge causes a break in the capping of the 

 scarp by the Mt. Gilmore toscanite, and also displaces the Martin's Creek andesite, 

 making a small break in the outcrop through which the Williams Eiver now 

 flows. 



The only reversed fault observed in the area is about half a mile north of 

 Martin's Creek Station. It brings the hypersthene-pitchstone against the hom- 

 blende-andesite and produces a peculiar tongue-shaped plan of outcrop of the 

 tuffs separating these two beds. It indicates movement from the west and it is 

 interesting to note the following mention by Prof. David (1904, p. 339) of 

 faults in the Hunter River area to the south: "The faulting in almost every case 

 is of the nature of normal faulting; such rare overthi-usts as do occur show 

 evidence of a thrust from the west." 



General Considerations concerning the Faulting and Folding. 



In the area under discussion there are five large faults all striking within the 

 interval N — N. 30° E., three faults with smaller throws and a general east-west 

 trend, and numerous small dislocations including an underthrust whose features 

 are not of great significance. 



In many areas the existence of two sets of faults with trends at right angles 

 to one another indicates two periods of fracture, often separated by a wide in- 

 terval of time, and in the area under description such a possibility must be con- 

 sidered. But it is also possible that the variable composition and resistance of 

 the rocks and the peculiarity of the folded structures may have determined the 

 positions of minor faults such as those that do not strike north and south in this 

 case, and therefore that the whole of the faulting could have been the outcome 

 of the same impression of diastrophic force. Also one should observe that the 

 three faults of general east-west orientation all show up as physiographic features, 

 for which reason a Tertiary age might be assigned to them. 



The writer has been unable to decide whether or not there have been two 

 distinct periods of faulting. 



It is almost beyond doubt that the large meridional faults are pre-Mesozoie 

 in ag-e for the following reasons: — The faults show no direct physiographic ex- 

 pression or control. Indirectly they affect the topography in having arranged 

 the hard and soft strata in certain patterns, but no scarps belonging to them 

 exist, and there is dii-ect evidence that the area was faulted by the north-south 



