148 



L. A. COTTON. 



corresponds to 20th October, 1915 



1 „ 18th January, 1916 



2 „ 17th February, „ 



3 „ 27th May, 



4 „ 4th October, „ 



5 „ 23rd November, „ 



6 „ 22nd January, 1917 



7 „ 2nd May „ 



8 „ 9th October, „ 



9 „ 8th April, 1918 



10 „ 17th July, 



11 „ 25th October, „ 



12 „ 2nd February, 1919 



The deflections are all referred to station of the 20th 

 of October, 1915, as the standard of reference. The east 

 and west deflections are measured horizontally, and the 

 north and south deflections vertically as shown by the 

 cardinal points on the diagram. The deflections are 

 measured in seconds of arc. In order to obtain the direc- 

 tion and amount of the tilt corresponding to any of the 

 points marked 1, 2, etc., the following procedure is adopted: 

 Take for example the deflection for the 8th of April, 1918, 

 as recorded at station 9. Join 9 to 0. The length of the 

 joining line is 6*74 divisions and therefore represents a 

 deflection of 6*74 seconds of arc. The angle made by the 

 line joining and 9 with the horizontal or east direction 

 can be measured with a protractor (or calculated from the 

 tangent relation) and is thus seen to be 10J degrees. The 

 tilt is therefore 6*74 seconds in a direction east lOf degrees 

 south. Similarly for station 2 the tilt can be shown to be 

 2*07 seconds in a direction north 12£ degrees east; and so on. 



The amount of tilting is very surprising and suggests 

 that the rocks are undergoing great strain as the result of 

 temperature changes. Hence it is possible that the effect 



