76 Scientific Intelligence. 



the supervision of Prof, David has reached a depth of 643 feet. 

 In regard to the deposits passed through, three zones have been 

 recognized. The first extended to a depth of 200 feet; of this 

 40 feet were made up of coral reef rock and below the material 

 was also largely derived from corals with brief interludes of true 

 reef. The second zone, from 200 to 373 feet, consisted largely of 

 sandy material, sometimes a calcareous mud, with occasional coral 

 fragments. These deposits are not reef but were doubtless 

 formed in the neighborhood of a reef. The third, or lowest, zone 

 corresponds apparently to the first ; the character of the material 

 suggested that it was formed near a reef which occasionally 

 extended out laterally, building up layers of true reef upon 

 detrital coral. Much of the rock pierced at this depih was a 

 hard and compact coral limestone. 



Prof. David, though not attempting as yet to discuss the theo- 

 retical bearing of the facts obtained, remarks that they prove 

 that true reef has been pierced to a depth of more than 600 feet. 

 Further, for the whole time represented coral must have been 

 growing in great abundance in some part of the locality now 

 represented by Funafuti, the atoll being completely isolated from 

 all other coraliferous localities. 



5. Origin of the Diamonds of South Africa. — In an article in 

 recent numbers of the Geological Magazine, describing some rock 

 specimens from Kimberley, South Africa, T. G. Bonney presents 

 his conclusions in regard to the origin of the diamonds and the 

 volcanic phenomena of the region as follows: 



I believe, as I have already stated, that the diamonds were not 

 produced where they are now discovered, but, like the conspicu- 

 ous olivine, pyroxenes, mica, garnets, and iron-oxides, had their 

 origin at a much greater depth in the earth's crust. Thus I think 

 it improbable that the carbon was obtained from the Karoo 

 Shales. In other words, I consider the diamonds, whatever may 

 have been their past history, to have come from the crystalline 

 floor on which these shales were deposited, or to be at any rate 

 Pre Triassic in age. I see no reason why carbon should not be 

 present in the earth's magma, whether it afterwards crystallized 

 in a peridotite or in native iron. 



Volcanic action probably began before the end of the Karoo 

 epoch, as the great sheet of so-called melaphyre seems to be in- 

 tercalated with its higher deposits, and some of the dykes may 

 be approximately coeval with it. Afterwards (was it because of 

 this impenetrable cover of lava?) the pipes were formed, probably 

 in a short time, by a series of great explosions, caused by gases 

 accumulated at considerable depth. These sent the outer part of 

 the crystalline floor, including the diamonds, as well as the over- 

 lying Karoo shales, flying shattered into the air. Cones and 

 craters may have been built up above these pipes, but I expect 

 that, like some of those in the Eifel, they were never high, and 

 that the shattered material mostly fell back, after a few explo- 

 sions, into the pipes and filled them like the " necks " in Scotland. 



