Magnetic Survey of Natal. ^7 



of this particular ridge line, Umhlatuzi, Greytown, Albert Falls, 

 Dargle Road and Boston, all to the north of it, have horizontal 

 intensities greater than the average, whereas Grange, Camperdown, 

 Dalton, Stanger and Tugela, on the south, have values less than the 

 normal. 



The dips to the north and the south of such a line of attraction 

 will be less and greater respectively than the normal values. The 

 dips at the above stations are such as to be in agreement with the 

 suggested position of the ridge line, except in the case of Boston. 

 The explanation of the difference in this case is probably due to 

 the cross ridge line — which passes north of Underberg — continuing 

 east to the north of Boston. 



The second part of the Natal-Zululand ridge line is not so 

 certainly marked ; its position throughout a considerable part of 

 its length depends on observations at a single line of stations only. 

 Here the ridge of magnetised matter runs north and south, and — the 

 declination being west — stations to the east of such a line ought to 

 have a declination less than the average, stations to* the west a 

 greater declination. Boston, Fountain Hall, Estcourt, Colenso and 

 Dannhauser have declinations smaller than is to be expected, and 

 therefore lie to the east of the line, Modderspruit and Waschbank 

 greater values, thus fixing their position to the west. The directions 

 of the disturbing horizontal forces support this, with the exception 

 of that at Modderspruit ; there, instead of being directed towards 

 the ridge line, as drawn from the declination results, it is directed 

 away from it. At that point there is, therefore, an ambiguity in 

 the position of the ridge line. 



The valley line which starts between Modderspruit and Wasch- 

 bank begins at a col — that is, a point on a ridge line where the 

 vertical force has a minimum value ; the existence of such a line 

 is supported by the value of the declination at Greytown, which is 

 greater than the normal, and which, therefore, is to the east of a 

 valley line. This valley line probably continues through Dalton, 

 east of Krantzkloof and west of Durban. 



The Griqualand East and Natal valley line separates a region 

 of higher horizontal intensity on the south from one of lower in the 

 north. The dip results are also strongly in support of this line being 

 considerably lower to the south and higher to the north. In the 

 case of all the stations in the neighbourhood of this line the direction 

 of the horizontal disturbing forces is — as it is to be expected — away 

 from it, with the one exception of Richmond. 



