274 
mi. A. W. RUCKER AND DR. T. E, THORPE ON A MAGNETIC 
Surveys or Selected Districts. 
Having described and, as we hope, justified the methods by which we propose to 
investigate local and regional disturbances, we now proceed to discuss their applica¬ 
tion to districts of which we have made a special study. The results we shall arrive 
at will help us in the further elucidation of the magnetic state of the whole country. 
The Malvern Hills. 
The general nature and direction of the magnetization of igneous rocks is a problem 
on which comparatively few observations have been made. It is, indeed, known that 
when examined in detail they present great irregularities, and Commander Creak, 
F.R.S., has shown (‘Hoy. Soc. Proc.,’ vol. 40, 1886, p. 83) that when islands disturb 
the magnetic needle in the northern hemisphere they attract, and in the southern 
repel the north-seeking pole of a magnet. This is what would be expected if they 
were the upper extremities of magnetic masses magnetized by the Earth’s induction. 
In like manner in Sweden, where (as has already been stated) the method of 
searching for iron ore by means of the magnet has been carried to considerable 
perfection, the assumption made, and justified by experience, is that tlie upper parts 
of the beds of ironstone attract the north-seeking pole. 
Observations somewhat similar to those of Commander Creak can be carried out 
on land in cases where igneous rocks rise in the midst of sedimentary deposits, and 
such observations are sj)ecially interesting in cases, such as that of the Malvern Hills, 
in which the axis of the magnetic mass runs north and south. 
If its depth is considerable with respect to its length, and if it is magnetized by 
induction, we should expect the upper visilde parts to attract (in the northern hemi¬ 
sphere) the north-seeking pole. If, on the other hand, it is possible to conceive of a 
shallow mass of magnetic rock surrounded by non-magnetic matter, the northern end 
might repel the north-seeking pole. Finally, if the mass was itself magnetized 
independently of the present inductive action of the Earth, as is certainly the case 
with small masses of highly magnetized lodestone, its effect on a compass needle could 
only be determined by experiment. 
With tlie view, then, of making a beginning towards the study of these questions 
in the United Kingdom, we determined the polarity of the northern end of the 
Malvern Hills. 
This range consists of syenite and granite. The mass of igneous rocks runs due 
north and south for about eight miles, and is at the broadest part but little more 
than half a mile wide. On its eastern side is a great fault which extends many miles 
north and south of the range itself. Two stations. Great Malvern (1126) and Malvern 
Wells (112c), were taken on the eastern side of the hills. They were both on the Red 
Marl, and distant aljout a mile and a quarter from the centre of the range. Two 
