May 30, 1918] 



NATURE 



257 



was and puts the burden of' an explanation upon the 

 unknown conditions and laws which exist insidt- the 

 atom. I have already given reasons for discrediting- 

 ilie first type of theory. The second type, though as 

 \ (>t very incomplete, seems to me to be the only possible 

 '>ne, and it has already met with some notable suc- 

 it^sses, as in -the case of the Bohr atom. Yet the 

 rlifory is at present woefully incomplete and hazy. 

 About all that we can say now is that we seem to be 

 driven by newly discovered relations in the field of 

 radiation either to the Thomson-Einstein semi-corpus- 

 rular theory, or else to a theory which is equally 

 subversive of the established order of things in physics. 

 lor either one of these alternatives brings us to a 



\olutionary quantum theory of radiation— that 

 a theory which calls for an explosive emission of 



■ rgy in units and has therefore something akin 

 atomism about it. To be living in a period 



hich faces such a complete reconstruction of our 

 notions as to the way in which aether waves are 

 absorbed and emitted by matter is an inspiring pros- 

 pect. The atomic and electronic worlds have revealed 

 themselves with beautiful definiteness and wonderful 

 corrsistency to the eye of the modern physicist, but 

 their relation to the world of aether waves is still to 

 him a profound mystery for which the coming genera- 

 tion has the incomparable opportunity of finding a 

 solution. 



CliOLOGICAL STRUCTURE IN RELATION 

 TO MAGNETIC DISTURBANCE. 



. A LPXTURE on the relationship between geological 

 -^^ structure and magnetic disturbance, with especial 

 reference to Leicestershire and the concealed coalfield 

 of Nottinghamshire, was delivered before the Geo- 

 logical Society on May i by Dr. A. Hubert Cox. 



Before the lecture, at the request of the president, 

 Dr. A. Strahan, director of the Geological Survey, 

 briefly outlined the circumstances that had led to an 

 investigation into a possible connection between geo- 

 logical structure and magnetic disturbances. The 

 magnetic surveys conducted by Riicker and Thorpe 

 in 1886 and 189 1 had proved the existence of certain 

 lines and centres of disturbance, but those authors 

 observed that "the magnetic indications appear to be 

 quite independent of the disposition of the newer 

 strata," and Dr. Strahan had not been able to detect 

 any obvious connection with the form and structure 

 of the Palaeozoic rocks below. In 1914-15 a new 

 magnetic survey was made by Mr. G. W. Walker, 

 who confirmed the existence of certain areas of dis- 

 turbance. It was suggested that the effects might be 

 due to concealed masses of iron ore, and the. matter 

 was referred to the Conjoint Board of Scientific Socie- 

 ties, which appointed an Iron Ores Committee to con- 

 sider what further steps should be taken. The com- 

 mittee recommended that attention should be concen- 

 trated on certain areas of marked magnetic disturb- 

 ance, and that a more detailed magnetic survey of 

 these areaSi accompanied by a petrological survey and 

 an examination of the magnetic properties of the 

 rocks of the neighbourhood, should be made. Dr. 

 Strahan had been approached with a view to the petro- 

 logical work being undertaken by the Geological 

 Survey, and it had been arranged by the Board of 

 Education, with the consent of H.M. Treasury, that 

 a geologist should be temporarily appointed as a 

 member of the staff for the purposes of the investiga- 

 tion. Dr. Cox had received the appointment, and his 

 lecture would show that results of great significance 

 had been obtained by him. The new magnetic ob- 

 servations had been made by Mr. Walker, and the 

 examination of the specimens colWcled. in regard to 

 NO. 2535, VOL. lOl] 



their magnetic susceptibility, had been conducted bv 

 Prof. Ernest Wilson. 



Dr. Cox then described the selected areas, which 

 lay on Lias and Keuper Marl between Melton Mow- 

 bray and Nottingham, and in the neighbourhood of 

 Irthlingborough, where the Northampton Sands are 

 being worked as iron ores. The Middle Lias iron 

 ores, consisting essentially of limonite, which crop 

 out near Melton Mowbray, have been proved in- 

 capable, by reason of their low magnetic suscepti- 

 bility, of causing disturbances of the magnitudes 

 observed, while the distribution of the disturbances 

 showed no correspondence with the outcrop of the 

 iron ores. Nor was any other formation among the 

 Secondary rocks found capable of exerting any ap- 

 preciable influence. It appeared, therefore, that the 

 origin of the magnetic disturbances must be deep- 

 seated. 



Investigation showed that the disturbances were 

 arranged along the lines. of a system of faults rang- 

 ing in direction from north-west to nearly west. 

 The faults near Melton Mowbray have not been 

 proved in the Palaeozoic rocks, and, so far as their 

 effects on the Secondary rocks are concerned, they 

 would appear to be only minor dislocations. But 

 farther, north, near Nottingham, faults which take a 

 parallel course, and probably belong to the same 

 system of faulting as those near Melton Mowbray, 

 are known from evidence obtained in underground 

 workings to have a much greater throw in the Goal 

 Measures than in the Permian and Triassic rocks 

 at the surface. It appears, therefore, that movement 

 took place along the same lines at more than one 

 period, the earlier and more powerful movement being 

 of post-Carboniferous but pre-Permian age, the later 

 movement being post-Triassic. Accordmgly, it is 

 probable that the small dislocations in the Mesozoic 

 rocks indicate the presence of important faults in the 

 underlying Palaeozoic. 



The faults can give rise to magnetic disturbances 

 only if they are associated with rocks of high mag- 

 netic susceptibility. It is known from deep borings 

 that the concealed coalfield of Nottinghamshire ex- 

 tends into Leicestershire, but how far is not known. 

 Deep borings have proved that intrusions of dolerite 

 occur in the Coal Measures at several localities in 

 the south-eastern portion of the concealed coalfield, 

 and always, so far as observed, in the immediate 

 vicinity of faults. It has been established that 

 dolerites may exert a considerable magnetic effect; 

 and the susceptibility *of those that occur in the Coal 

 Measures is above the general average. Further, no 

 other rocks that are known to occur, or are likely 

 to occur under the area, have susceptibilities so high 

 as the dolerites found in the Coal Measures. These 

 facts suggest the possibility of the occurrence of 

 dolerites intrusive into Coal Measures beneath the 

 Mesozoic rocks of the Melton Mowbray district. 



The distribution of the dolerites actually proved, 

 and of those the presence of which is suspected by 

 reason of the magnetic disturbances, appears to be 

 controlled by the faulting. Moreover, whereas the 

 character of the magnetic disturbances is such that it 

 would not be explained by a sill or laccolite faulted 

 down to the north, in the manner demanded by the 

 observed throw of the principal fault, it would be 

 explained by an intrusion that had arisen along the 

 fault-plane. The faulting itself is connected with a 

 change of strike in the concealed Coal Measures, and 

 the incoming of doleritic intrusions in the concealed 

 coalfield, in contrast with their absence from the 

 exposed coalfield, appears to depend upon the changed 

 tectonic features. The change of strike is apparent, 

 but to a less degree, in the Mesozoic rocks, which; in 

 the neighbourhood of Melton Mcv^vbray, have suffere<l 



