December 29, 1923] 



NA TURE 



939 



probable that Africa has always been on one side 

 of the equation. But one would expect that, had the 

 continent been " predominantly in a state of tension," 

 evidence of the fact would not be difficult to find in 

 Uganda. 



True, there is no reason why " a change of con- 

 ditions may not convert a true rift valley formed in 

 a period of tension into one bounded by reversed 

 faults." But it may also be observed that it is certain 

 that tension operating on a rift formed by a thrust 

 action would accentuate the features, provided that 

 the bottom of the valley was not prevented by 

 subterranean support from sinking. Compression 

 would do the same without the last proviso ; while 

 some such factor as cooling at depth would achieve a 

 similar result without the assistance of either tension 

 or compression if the faults were reversed. 



There can be no shadow of a doubt that the bottoms 

 of the Uganda rift valleys have sunk, and that, too, 

 very considerably. What has happened beyond this 

 it is impossible for any living soul to say with absolute 

 certainty at present ; but no theory of the rift will 

 pass muster if it leaves Ruwenzori hanging in the 

 air, and if it fails to explain why planes of weakness 

 to tension have not- been utilised. 



Assuming a rift-block (by which I mean the mass 

 between the rift features) bounded by reversed faults 

 to sink, something must happen to the valley sides ; 

 either one or both will subside as a whole, or great 

 lines of normal faulting will appear in the country on 

 one or both sides ; or these two things may happen 

 in combination. The first of these alternatives 

 appears, almost to the entire exclusion of the second, 

 by Lake Albert, in Bunyoro ; the second, largely to 

 the exclusion of the first, is seen along the eastern 

 side of Lake George. Moreover, normal faulting may 

 appear in the rift-block itself. But all these things 

 may equally be consequent upon settlement of a 

 rift-block bounded by normal faults. Thus it is 

 easily seen that step faulting is not admissible as 

 evidence as to the nature of the fractures that initiated 

 the rift. The solution of the Great Rift Valley problem 

 must be sought, in fact, in places like Bunyoro, where 

 step faulting is almost completely absent. 



Dr. Evans, who combines Wegener's general 

 proposition with a tentative theory of the moon's 

 birth, would expect (subject to the truth of the latter) 

 " The chief period of tension in Africa and its sur- 

 roundings to have existed in Mesozoic and early 

 Kainozoic times " ; but this is precisely when, so 

 Prof. J. W. Gregory argues (and I agree with him), 

 Africa was being hunched up by compression. 



As to the date of the moon's birth, or the manner 

 of it, I am not qualified to speak with any authority ; 

 but I should have thought that had it taken place as 

 late as the Carboniferous period, the parting at least 

 would have been catastrophic. Also I am tempted 

 to ask (not controversially, but as one seeking in- 

 formation) why if " the bulk of the atmosphere " was 

 " attracted towards the protruding mass of the moon," 

 our satellite has now no atmosphere worth mentioning. 

 Did the moon escape without air or water ; or may it 

 not be that it once f)ossessed both, self -elaborated very 

 long ago, as those of the earth, in an early stage of 

 its individual career ? May not the absence of 

 atmosphere be indicative of completion in the life of 

 a celestial body of a stage the span of which is a 

 function of the sphere's mass ? 



I fear that I have somehow created the impression 

 that all the major faulting in this part of the world 

 is more or less north and south. Ihis is not so. In 

 Bunyoro certainly, and one has reason to believe 

 elsewhere, a series of very large east to west faults is 

 traceable. This is clearly brought out in a structure 



NO. 2826, VOL. 112] 



map of part of Bunyoro prepared by Mr. W. C. 

 Simmons a few years ago. Judging by the manner in 

 which they cut off the north to south fractures, the 

 east to west faults are the younger ; though both 

 are very ancient. 



I believe that the word " rift " was originally 

 applied to the Great East African fracture trough, 

 which is quite a different thing from an ocean-covered 

 area produced by the drifting of continents. Rift 

 valley faults will still remain rift valley faults, whether 

 they turn out to be normal or reversed ; otherwise 

 " rift valley " must disappear from our nomenclature 

 should my hypothesis prove true. 



I thoroughly agree with Dr. Evans's remarks with 

 regard to the value of speculative hypothesis ; and, 

 as he reminds us, " It will only be when we have all 

 the facts before us, that we shall be able to solve with 

 any assurance the problems presented by the present 

 configuration of the surface of the globe." 



E. J. Wayland. 



Mahyuro, Lake George, Uganda, 

 November 3. 



Mrs. Hertha Ayrton. 



In Nature of December i there appears under the 

 above heading an obituary notice of the late Mrs. 

 Ayrton which, I regret to say, is in some matters 

 incorrect and misleading. The article is an unusual 

 one, for in it the writer ventilates his own grievances 

 against his so-called " masters " (The City and Guilds 

 Institute), and disparages and belittles the work and 

 abilities of his lifelong colleagues. To write in this 

 strain about dead friends is in my opinion reprehen- 

 sible, and it is to be hoped the example will not be 

 followed. 



From reading Prof. Armstrong's article one would 

 gather that Mrs. Ayrton had little originality, and that 

 all the scientific work she did was due to her husband's 

 lead. Neither inference would be true, as is proved by 

 the inventions she made before she met Prof. Ayrton 

 and the original work she carried out after his death. 

 In connexion with the latter, Mrs. Ayrton took out 

 eight patents between 1913 and 1918. 



The late Prof. Ayrton told me on several occasions 

 that when Mrs. Ayrton took up the study of the 

 electric arc he left the subject entirely alone so that 

 there should be no excuse for any one giving him the 

 credit for her work, and when lecturing to his students 

 on the arc he made similar statements, as many of his 

 pupils can doubtless confirm ; it is indeed very prob- 

 able that Prof. Armstrong heard analogous remarks 

 from Prof. Ayrton's own lips. T. Mather. 



37 Wyatt Park Rd., 

 Streatham Hill, S.W.2, 

 December 10. 



A Waltzing Mouse. 



It may perhaps be of interest to record that, in 

 some recent experiments in crossing mice, there 

 appeared in a litter of seven (self-coloured champagne) 

 a female which exhibited all the symptoms as.sociated 

 with the Japanese waltzing mouse of which Yerkes 

 made a fairly exhaustive study. It is dextro- 

 rotatory, if the term be permitted. It is not yet 

 old enough for reproduction. Both parents have, 

 however, since produced litters, the female to a 

 Dutch-marked male, the male on a Dutch-marked 

 female, five and four respectively, but all are normal, 

 nor out of eighty mice recently born to other couples 

 have I had any other that waltzes. 



G. W. Harris. 



The Royal Automobile Club, London, S.W.i, 

 November 25. 



