1 86 The American Geologist. March, is99 
by de Laimay, Lewis, and Crookes.* De Launay describes 
the serpentine of the Kimberley mines of South Africa as be- 
ing derived from a peridotyte determined by Stelzner as a 
picrite-porphyry. Mixed with the serpentine are abundant 
fragments of various rocks, so that many specimens are of the 
nature of a contact-breccia. These serpentine bodies occur 
as pipes or phigs extending down nearly vertically to an un- 
known deptii. The general shape of the section of each pipe 
at the surface is round or oval. In following the volcanic 
plugs (\pwn it has been proven that each one passes through 
several formations. At the surface the enclosing rocks are 
( arbonaceous shales, and at one time it was believed that the 
carbon composing the diamonds was primarily derived from 
these shales, and when the excavations passed through the 
carbonaceous shale it was feared that diamonds would no long- 
er be found. Underlying the shales is a bed of diabase. The 
serpentine at this horizon still contained diamonds as before. 
At the present time the excavations or shafts at Kimberley 
and De Beers have gone through the diabase horizon and 
the miners are now engaged in working the volcanic pipes in 
the underlying quartzytes. De Launay states that the en- 
closing terranes have had no influence whatever either on the 
quantity or the quality of the diamonds. These have incon- 
testably come from below with the peridotyte-breccia. The 
idea that the carbon of the diamonds came from the upper 
carbonaceous shales is thus disproven. Moreover, there are 
very numerous volcanic chimneys of the peridotyte (kimber- 
lyte) in South Africa, and not all of these contain diamonds, 
while some contain them only rarely or of microscopic sizes. 
De Launay states that the cavities which contain the ser- 
pentine pipes are of the nature of volcanic chimneys. Water 
l)enetrating to the contact of a molten metallic bath charged 
with various carburets, caused the sudden formation of car- 
burets of hydrogen, and by their explosion the opening of the 
volcanic chimneys. The water produced the scorification of 
the molten peridotyte magma, and by the compression thus 
exercised on the carbon, the crystallization of the diamonds. 
*L. de Launay, "Lcs Diamants du Cap," Paris. 1897; H. C. Lewis. 
"Genesis and Matrix of the Diamond," London, New York, and Bom- 
hay, 1897; Sir William Crookes "Diamonds," Proceedings of the Royal 
Institution, Vol. XV, 1897, pp. 477-501. 
