April 8, 1920] 



NATURE 



175 



years of a devastating world war, and in this task 

 of extending- our knowledge of pure science and 

 its application to the whole field of industry the 

 Imperial College is called upon to play a vital and 

 predominant part. 



The recognition of how great and important are 

 the responsibilities thus cast upon the Imperial 

 College has led to a movement for obtaining for 

 the college the status of a university with the 

 power to confer degrees in its own subjects or 

 faculties. The movement is backed by the unani- 

 mous support of the rector and professors of the 



Imperial College, and it is supported, so far as 

 can be ascertained in any organised way, by the 

 overwhelming majority of the past and present 

 students of the college. The issue raises, no 

 doubt, questions that are novel and complicated 

 in relation to university education in general and 

 to the University of London in particular. Nothing 

 but good can come from a free and frank examina- 

 tion of the proposition in all its bearings, undis- 

 turbed and unprejudiced by lesser interests than 

 that of increasing the efficiency of university 

 education and especially of scientific education. 



Magnetic Disturbances 



T^HE research described in the report before us 

 •*• was undertaken at the instigation of the Iron 

 Ores Committee of the Conjoint Board of Scien- 

 tific Societies. Certain lines and centres of mag- 

 netic disturbance had been noted in Britain so 

 long ago as 1890 by Rucker and Thorpe, and a 

 new magnetic survey by Mr. G. W. Walker in 

 the years 1914 and 191 5 confirmed the existence 

 of these disturbed areas. It is well known that 

 iron is the only element which gives rise to mag- 

 netic effects of considerable intensity, and it was 

 therefore of importance to determine whether any 

 relationship could be established between the loca- 

 tion of these disturbances and the distribution of 

 iron ores. 



The detailed magnetic survey of (i) the proved 

 sheet of iron ore, mainly in the state of ferrous 

 carbonate, round Irthlingborough, and (2) the 

 known areas of magnetic disturbance about 

 Melton Mowbray, was therefore undertaken by 

 Mr. Walker. At the same time. Dr. Cox reviewed 

 the geology of the areas and collected specimens 

 of rocks which promised to afford evidence in the 

 matter, while the magnetic susceptibilities of 

 these materials were determined by Prof. Ernest 

 Wilson. 



The results of the magnetic and petrological 

 examination of the rocks confirm the opinion that 

 the magnetic susceptibility of rocks depends 

 scarcely at all upon the percentage of metallic 

 iron they contain, but upon the condition — i.e. 

 state of oxidation — of that iron ; and that, 

 although rocks composed of ferrous compounds 

 show higher susceptibilities than those constituted 

 of fully oxidised ferric compounds, only those 

 rocks in which the iron occurs as the mineral 

 magnetite have notable magnetic susceptibility. 

 It was shown that parts of the granite of Mount 

 Sorrel have a susceptibility more than four times 

 as great as that of the most magnetic of the local 

 Jurassic iron ores, and ten to fifteen times as 

 great as certain basic igneous rocks, which, 

 though high in iron, contain no appreciable 

 amount of magnetite. 



Another point of some interest is the variability 

 of magnetic properties shown by samples taken 

 from one continuous rock mass. The outer part 



1 "A Report on Magnetic Disturbances in Northamptonshire and 

 Leicestershire and their Relations to the Geological Structure." By Dr. 

 A. H. Cox. Phil. Trans. Key. Soc, Series A, vol. ccxix., pp. 73-135 ; 



plates A p. i.-Ap. iii. 



NO. 2632, VOL. 105] 



and Geological Structure.^ 



of the dolerite sill proved in the Owthorpe borehole 

 was a fine-grained rock having a glassy base ; its 

 iron ore occurs as magnetite, and the magnetic 

 susceptibility of the specimen examined was 

 472 X 10-5 C.G.S. units. The coarse-grained rock 

 from the centre of the intrusion, however, in 

 which the iron ores crystallised as ilmenite, gave 

 a susceptibility of only 10-3x10-^ C.G.S. units. 

 A like low susceptibility was noted also in the 

 basalt from the Southwell borehole. 



The magnetic phenomena of the Irthlingborough 

 district are adequately explained by the presence 

 of such a large, flat-lying sheet of feebly magnetic 

 rock as the Bajocian iron-ore bed, but in the 

 Melton Mowbray district the proved limits of the 

 marlstone iron-ore bed bear no relation to the 

 observed magnetic phenomena. Moreover, the 

 consideration of the magnetic irregularities 

 obtained in the Melton Mowbray district shows 

 that the source of the disturbance cannot be less 

 than 3000 ft., and may be as much as 10,000 ft. 

 beneath the surface. The only rocks in this 

 region which have the requisite magnetic suscept- 

 ibility and may be expected to occur at these 

 depths are dolerites, such as are found intrusive 

 into the Coal Measures throughout the Midland 

 coalfield area, or possibly granites like those 

 which have invaded the old pre-Carboniferous 

 rocks in Charnwood Forest. 



Mr, Walker's observations show that, near to 

 Melton Mowbray, there are two main magnetic 

 disturbances, and that the line joining them 

 ranges north of west and south of east from 

 Melton Mowbray towards Rempstone, passing a 

 little south of the latter place. This line agrees 

 with that of a known fault of small throw which 

 cuts the Mesozoic rocks, and may be expected to 

 have a much larger throw in the Palaeozoic and 

 older strata underground. Similar magnetic dis- 

 turbances are noted near certain large faults in 

 the Nottingham district. Rucker and Thorpe 

 showed that magnetic disturbances are always to 

 be expected where a sill or dyke of highly 

 susceptible rock is displaced by a fault, and that, 

 if any rock containing magnetite is intruded as 

 a dyke among non-susceptible rocks, similar 

 magnetic disturbances must occur. It is known 

 that in many districts the place of intrusions has 

 been determined by faulting, and it is pointed out 

 by Dr. Cox that the concealed coalfield of Notting- 



