86 L. A. COTTON. 



to find a good exposure of the fault plane and to record the 

 dip which is an angle of 59° in a direction W. 14° S. 



Hence it appeared probable that the Kurrajong fault 

 may have been the origin of the shock and that the move- 

 ment was precipitated by tidal forces. 



In order to ascertain as accurately as possible the area 

 of greatest disturbance it was desirable to collect sufficient 

 information to enable the isoseismals to be drawn. The 

 following circular was therefore sent to the headmasters 

 of schools within an area, which, judging by the newspaper 

 accounts, seemed sufficient for the purpose: — 



"Geology Department, Sydney University, 

 18/8/19. 

 The Headmaster. Public School 



Dear Sir, — You have no doubt heard of the earthquake which 

 was felt in the Sydney district on Friday night last. The shock 

 occurred at 821 p.m. and appears to have been felt over a con- 

 siderable area. In view of the rarity of such shocks in the past 

 it is very important to obtain full and accurate data of this earth- 

 quake. One looks naturally to a teacher as the most capable 

 investigator in such matters because of his educational training 

 The school, too, is an ideal centre of investigation as it reaches 

 practically every family and home in the district. Will you be 

 kind enough to assist in this question and so make a contribution 

 to the Advancement of Science ? 



It is important to collect as far as possible answers to the 

 following questions: — 



1. Was the earthquake generally felt by everyone in the district? 



2. Was it felt by people moving about out of doors? 



3. Was it felt only by people at rest indoors? 



4. Was it possible to estimate the direction in which the shaking 



took place ? 



5. Was the earthquake accompanied by any sound ? 



6. Was the sound heard before or after the shock was felt ? I 



