630 
MR. A. W. RtrCKER AND DR. T. E. THORPE ON A MAGNETIC 
District 13.— Mid- Wales. 
A ridge line runs from Stoke-upon-Trent to a point north of Builth, in the upper 
valley of the Wye. It passes close to the Wrekin, the largest Vertical Force Dis¬ 
turbance in the neighbourhood being at Wellington (Salop). 
The secondary ridge from Oswestry probably crosses this district and leaves it at 
Hay, where there is a magnetic col. 
Though interesting geologically, the magnetic characteristics of Mid-Wales are 
quite simple and clear. 
District 14.— Southern England and Wales. 
This great district includes the whole of those parts of England and Wales which 
have not yet been discussed, with the exception of a region near to the Bristol 
Channel, and of Devonshire and Cornwall. 
The northern boundary runs east from near Cardigan to Bromyard, then turns 
north for 70 miles to Ashbourne in Derbyshire, thence south to Northampton, and, 
after a somewhat tortuous course, finally reaches the sea again at Harwich. 
This agrees fairly with the result of our last survey, but Mid-Wales is now sepa¬ 
rated from the southern district, so that in Wales the valley line lies further south 
than that we previously drew. Birmingham was an anomalous station in our previous 
survey, and we suggested (“ 1890 Memoir,” p. 291) that this might be due to the 
existence of “ a district of high vertical force running from Birmingham northward.” 
This forecast has been verified, with the result that the main valley line has here 
been shifted northwards. 
Beginning the description of the district from the extreme north, we find that the 
Horizontal Disturbing Force at Burton-on-Trent is very small, and is anomalous in 
direction. A very curious horseshoe-shaped ridge line runs from Bromsgrove round 
Birmingham to Kenilworth. The evidence of the Vertical is strongly supported by 
the Horizontal Disturbing Forces. 
A very powerful centre of disturbance has been discovered at Stratford-on Avon, 
the Vertical Disturbing Force being the largest found south of Newmilns, in Ayrshire. 
The main ridge line is to the east of the town, and the peak is probably at its inter¬ 
section with the secondary ridge, which runs south from Melton Mowbray. South 
of Stratford-on-Avon the Vertical Disturbing Forces, though still large, diminish, 
and the Horizontal Forces begin to tend southwards. As the valley of the Thames 
is approached, the vertical disturbance again Increases, until the great ridge line is 
reached which crosses EnMand and Wales from the Thames to Haverford West. 
o 
The Vertical Disturbing Forces do not clearly indicate a magnetic connection 
betw^een Stratford-on-Avon and the Thames Valley. There is, however, some 
evidence of a secondary valley line running from Alcester to Moreton-in-the-Marsh 
and Cirencester, and the directions of the Horizontal Disturbing Forces are in accord 
