616 
ME. A. W. RtrCKER AiSTD DR. T. E. THORPE OX A MAGNETIC 
Thus, if we trace the line from the east, we find a clearly marked ridge running 
north and south, near Elgin. The low Vertical Force at Forres indicates the magnetic 
valley which divides it from the prolongation of the main line of the Great Glen. 
The ridge line, as drawn from the Vertical Force Disturbances, after running south 
for some 20 miles, trends to the west, towards the Boat of Garten. This change of 
direction is made still more evident by the Horizontal Disturbing Forces, which at 
six stations to the south of the ridge point nearly due north. From the Boat of 
Garten, the locus of Maximum Vertical Force Disturbance is continued through 
Temple (Urquhart), Glen Afric, and Loch Duich to the stations in Skye ; but, 
whereas the Horizontal Disturbing Forces at the two first-named places tend 
towmihs or to the east of the line of the Caledonian Canal, the centre of attraction 
which mainly aftects Loch Duich is to the west of that station. 
Hence, if the Skye and north Caledonian Canal Stations are to be regarded as 
lying on the same ridge line, they must be considered as peaks. 
The key to the magnetic constitution of this part of Scotland seems to be the fact 
that Fort Augustus is a magnetic col. This was clearly shown in our earlier 
paper, the Vertical Disturbing Force at tliat station, though high, being less than at 
Inverness to the north, or Banavie to the south (“ 1890 Memoir,” Plate 13). A station 
has now" been interposed betw’een Fort Augustus and each of these places. Temple 
(Urquhart) is about half w-ay from Fort Augustus to Inverness, and Loch Lochy 
about half way to Banavie. At both these stations the Vertical Force Disturbance is 
greater than at Fort Augustus, so that the position of the magnetic col is fixed 
more definitely than before as being in the immediate neighbourho od of that place. 
A clearly marked valley line of Minimum Vertical Disturbing Force runs from 
Pitlochrie to Fort Augustus. It is, however, only of secondary rank, as it does not 
form part of a boundar’y 'which completely encloses a region of high Vertical Force, 
but crosses such a region at Fort Augustus. This line is prolonged to Glen Afric, at 
wLich place, though the Vertical Disturbing Force is as large as 98 {i.e., 0‘0098 
metric unit), it is less than at Temple (Urquhart) on the one side (110), and than 
at Loch Duich (158) on the other. 
From Glen Afric it proceeds to Aclinashellach, w’here it joins a main valley line. 
The importance of this secondaiy line from Fort Augustus to Achnashellach would be 
much enhanced if a region of very low' Vertical Force w’ei'e discovered betw’een Glen 
Afric and Loch Duich. In that event, a complete separation w'ould be eftected 
betw'een the Skye and Great Glen districts. As it is, we have no choice but to follow 
the indications aftbrded by the Vertical Force, w hich are clearly in closest accord w’ith 
the view that a continuous ridge line connects these regions, This view' is also 
supported by the clear indications of a parallel secondary valley line running from 
Mallaig (L. Nevis) to Fort Augustus, and thus meeting that w'hich runs Irom 
Pitlochrie to the same place. This valley line niay be regarded as dividing the 
Caledonian Canal District into tw'O sub-districts, in the southern of which the ridge 
