62 Br. Mar loth, on the Origin of the [Mar. 31, 



No new centre of infection has been discovered up to the present 

 time, and this year a large area of vines surrounding the original 

 phylloxerised centres has received treatments of cultivation varying 

 from 24 to 60 grammes of Bisulphide per square metre. 



These treatments have been given a little late in the year, in order 

 to allow the development of the winter-egg — which I have not met 

 with here, but before the exodus of the winged form has begun. (*) 



ON THE OEIOIN OF THE DIAMOND-MINES OF SOUTH- 

 AFRICA.— By R. Maeloth, Ph.D. 



[Eead 1886, March 31.] 



More than fifteen years have elapsed since digging for diamonds 

 was started on the places still bearing the name of Diamond Fields, 

 although they are surrounded now by well populated cities. This 

 corner of Grriqualand West has become of the highest importance for 

 the whole of South Africa, but the more scientific question about the 

 origin of these wealth-producing mines has not been sufficiently 

 answered as yet. I do not pretend to give a new theory which 

 disposes of all the difficulties and all the doubts respecting the forma- 

 tion of the mines, but I hope that the following remarks may con- 

 tribute a little towards the solution of this problem, so that future 

 geologists, aided by a larger amount of observation, may succeed, 

 where we with our fragmentary knowledge thereof still fail. 



All those who take some interest in the question know that the 

 diamondiferous mineral, the blue ground of the digger, is found only 

 in funnel-shaped holes, the bottom of which has not been reached 

 yet. There are four such holes principally worked at present, but as 

 Kimberley Mine, where sinkings have been made down for a depth of 

 600 feet, is the best explored of all, I restrict myself to this mine. 



The general opinion as to its formation is, that the orifice has been 

 formed by volcanic forces, and that the blue has been upheaved from 

 a greater depth, transporting thus the diamonds to their present 

 place. However, this orifice is not the crater of a volcano, as has been 

 stated in various publications, for instance by Mr. Chaper in his book 

 ''Note sur la region diamantifere de I'Afrique australe." It is only 

 the pipe which connected the crater with the interior of the globe, and 

 the crater, if there was any at all, has been washed away during the 

 long denudation which altered entirely the surface of South Africa. 



So far the question is pretty clear ; but a more serious divergence of 

 opinions exists on the state in which the diamondiferous mineral came 

 to its present place. Some geologists, as for instance Mr. Dunn, who is 

 now in Australia, and Professor Cohen from Strassburg, declare it to 

 be an igneous product, a kind of lava, which filled out tliis volcanic 

 orifice and hardened there. They mention in favour of their theory 

 especially the nature of the mineral, which they class near to the 

 serpentine. But how, I must ask at once, is it then to bo explained, 

 that not a single bit of the numerous fragments of the various rocks 

 and shales, embedded in the blue, exhibits a sign of fusion or altera- 

 tion by heat ? This ought to bo certainly the case, if the blue stuff, 



(••) Tlio exodus of wiugod females begun on the 1311i of January, 1SS7, ft^d this 

 year on the 1st of the same month. 



