SURVEY OE THE BRITISH ISLES FOR THE EPOCH JANUARY 1, 1891. 629 
Yorkshire District by a very arbitrary boundary, which runs across a region of high 
Vertical Force from Leeds to Burnley. 
The southern boundary of the district is a valley line, which runs from Ivh 3 d, in 
North Wales, vid Whitchurch, Congleton, and Leicester, to Northampton, and thence 
turns north to Rockingham, where it joins tiie lines which have been already 
discussed. 
In the north, a ridge line runs almost due east from Southport to Rochdale, and 
joins near Huddersfield the secondary ridge line, which passes southwards through 
Harrogate.* 
The directions of the Horizontal Disturbing Forces at Preston and Garstang are 
anomalous, but, as usual in such cases, they are below the limit of the correct determi¬ 
nation of direction. To the south of Huddersfield the combined ridge lines run 
south through Derbyshire parallel to or coincident with the valley of the Derwent.* 
Thence it runs in a south-easterly direction via Alfreton and Bingham to Melton 
Mowbray, thus entering what in our previous paper w^e called the Leicestershire 
District, 
The direction of the Horizontal Disturbing Force at Bingham is anomalous, but it 
is too small to make the discrepancy of any importance. 
It may be remembered that in our previous survey we discovered that Melton 
Mowbray was the seat of powerful Disturbing Forces. We have therefore made fresh 
observations at other places in the neighbourhood, and have proved that it is the 
highest point on a ridge line which connects it magnetically with Derbyshire. Hiis 
line, however, runs more directly north and south than that suggested in our earlier 
and confessedly tentative discussion of this district (“ 1890 Memoir, p. 291). 
To the south of this group of stations the ridge line appears to be continued past 
Market Harborough to Diinchurch, and thus to be brought into connection with 
another district. 
District 12. —North Wales. 
The principal feature in this district is a clearly-marked centre of attraction near 
Snowdon. A ridge line runs from Amlwch, in Anglesea, to Barmouth, north of 
Cader Idris, The attraction directly towards this line is, however, subordinate to 
that exercised by the magnetic peak. In all probability it is crossed at right angles 
by another secondary ridge. Oswestry appears to be more or less isolated, but there 
is a magnetic col at Llanfyllin, and the secondary ridge line thus indicated runs into 
another district. 
* Some doubt is caused here by the fact that the Horizontal Force Distui-bance at Huddersfield is 
anomalous, and is directed away from Rochdale where the Vertical Force Disturbance is greater. The 
indications of the Horizontal and Vertical Forces being thus discordant, we have shown the two 
alternative ridge lines on Maps 12 and 13, following the Horizontal Forces on Map 13, and the Vertical 
Forces in ilap 12. 
