96 ‘Correspondence—A. R. Hunt. 
to weigh something in the scale against ‘‘an inspection of the 
minerals.” I fancy, too, that my acquaintance with the literature 
of the diamond is more extensive than Dr. Flett’s, in spite of my 
having been for years out of reach of a scientific library. I have also 
studied specimens from most of the important diamond localities that 
I have been unable to visit. And I can only record my conviction, 
after a review of all the facts, firstly, that the Somabula diamonds, as 
also those of Brazil, India, and New South Wales, are derived from 
quite a different source from that of the sapphire, topaz, chrysoberyl, 
staurolite, kyanite, etc., with which they are associated, as has indeed 
been actually proved in the case of New South Wales; and secondly, 
that there is nothing to contradict the idea that the ultrabasic rocks 
(‘blue-ground’ and its allies) are invariably the source of the diamond. 
The question is no mere academic one. I should be only too 
delighted to gain an opportunity of describing a new matrix for the 
diamond. This, however, is the position. I am every day asked for 
advice by prospectors, men whose livelihood depends on their success 
in finding mineral deposits of possible economic value. When con- 
sulted about diamonds, what is one to tell such men as these? In 
face of the fact that every South African mine (and there must be at 
least thirty now working) is in ‘ blue-ground,’ is one to advise them 
to look for diamonds in camualltee or kyanite schists? Some, through 
ignorance, have actually done work on such rocks—needless, to say, 
without finding any diamonds. I even know of a locality where 
staurolite, kyanite, tourmaline, garnet, and rutile can be got from 
a single specimen. Could one in good faith urge the spending of 
money on it in the hope of its developing into a diamond- mine ? 
I certainly do not think so myself, whatever cther people’s views 
may be. F. P. Mennett. 
Ruopesia Museum, BuLawayo. 
December 28th, 1906. 
MARINE RIPPLE-MARK.! 
Sir,—. . . . Will you permit me to point out that in Mrs. Ayrton’ s 
researches on Sand-ripples, so far as they concern geologists and 
marine ripple-mark, there are four experimental fallacies. Mrs. Ayrton 
describes her apparatus as follows: ‘‘In this trough, six feet long 
. the water, which is about a foot deep, is now ‘made to swing 
periodically backwards and forwards by means of an electro-motor”’ 
(Abstract of lecture to Section G at Cambridge in 1904). 
In the real thing we find a series of periodically oscillating waves 
moving in one direction over a fixed bottom, and expending themselves 
on a sandy shore. In Mrs. Ayrton’s experiment we have an oscillating 
bottom, perfect reflection from vertical ends, waves moving in opposite 
directions, and, as one result, stationary waves in the experimental 
tank. None of these four conditions obtain at sea, and Mrs. Ayrteon’s 
results and conclusions, interesting though they are to physicists, 
have practically no bearing on the phenomena of the sea-shore and 
the sea-bottom. A. R. Hoyt. 
SoutHwoop, Torauay. 
1 [Unavoidably delayed in publication by want of space.—Ep. Grou. Mac. ] 
