Rocks and Regional 



527 



MAGNETIC FLOOR 



Thus being over the outer edge of the trench, 3 is over the middle 

 of the trench, 6 over the edge of the plateau, and 15 over its centre. 

 The forces are expressed in terms of units of disturbing force or 

 O'OOOOl C.Gr.S. unit. Horizontal forces are positive which urge a 

 north-seeking pole towards the central plateau. Vertical forces are 

 positive which act downwards as above stated. 



Other disturbances my be imagined which give similar results. 

 If the central plateau stood alone, surrounded by non-magnetic 

 mutter, the mean range, as calculated above between the vertical 

 forces over it and those observed within the 60 kilom. (36 miles) of 

 its edge, would be 127. If the edge of the valley, instead of being 

 vertical, were vertical for 10 kilom, only, and then sloped upwards 

 with an inclination of 1 in 10, the range would be 107. 



