104 L. A. COTTON. 



latter extends is however practically unknown from the 

 geological point of view, and for the most part is a very 

 rugged and sparsely inhabited region. Professor David 

 has pointed out to me that the direction of this western 

 limb of the isoseismals corresponds to that of a very 

 important fault system in the Maitland area, and that it is 

 moreover nearly coincident in both direction and actual 

 position with the trough of the Permo-Oarboniferous and 

 Triassic geosyncline, which is the major structural feature 

 of the area affected by the earthquake shock. (3) 



As far as the writer knows this is the first earthquake 

 which lias been interpreted in this way. The principles 

 involved are simple and of general application, and on 

 physiographic and theoretical grounds such a type of fault- 

 ing may be of relatively common occurrence. It is hoped 

 that the emphasis placed on the geological aspect may lead 

 to a more detailed and careful study of the distribution of 

 isoseismals in the case of other earthquakes. 



Acknowledgements. 

 The writer's warmest thanks are offered to the many 

 correspondents who very kindly, often at great personal 

 inconvenience, collected and forwarded information with 

 regard to the Sydney earthquake. Without such cordial 

 co-operation the work could not have been undertaken. 



Best thanks are also due to the Rev. Father Pigot, s.J., 

 and to Professor Cooke for kind permission to examine the 

 seismograms of the earthquake recorded at River view and 

 the Sydney Observatory respectively. 

 Bibliography. 



(1) B banner, J. 0. — Bull. Seism. Soc. Am., 1917. 



(2) David, T. W. E. — An important Geological Fault at Kurra- 

 jong Heights, New South Wales. Proc. Roy. Soc. N.S.W., 

 Vol. 36, 1902, pp. 359-370. 



(3) David, T. VV. E.— The Geology of the Hunter River Coal 



Measures. Mem. Geol. Surv. N.S.W., No. 4, 1907. 



(4) Omori, F. — Horizontal Pendulum Observation of Earthquakes 



at Hitotsubashi (Tokyo). Pub. Eqke. Inv. Com., No. 13, 1903. 



(5) Report of the Seismolo^ical Committee. Aust. Ass. Adv. 



Sci., Vol. 4, 1892, pp. 200-232. 



