Correspondence—F. P. Mennell. 95 
a direction at right angles to the stream, and in it were found the 
specimens described by Von Rath. In the decade 1890-1900 a little 
work was done each Summer, resulting in the specimens studied by 
Baumhauer. Since 1900 Francis Jentsch and his partners have 
worked the quarry regularly each Summer. In 1902 they came across 
the old tunnel constructed in 1731, the existence of which had been 
quite forgotten. Up to 1898 eighteen mineral species had been found, 
of which four are peculiar to the quarry; since that date twenty-five 
* additional species, of which no fewer than twenty are new to science, 
have come to light. Nine of the new species have been named, two 
are pseudomorphs, and nine, owing to paucity of material. have not yet 
been described. The minerals found this year include Trechmannite 
fine crystals), Baumhauerite (curiously striated and distorted crystals), 
seligmannite (a large crystal 20mm. in length), Jordanite (a twin 
about 301), Dufrenoysite (a twin about 001), pseudomorphs of 
Dolomite and Baumhauerite after Scapolite (?).—Note on the ‘Thirty- 
two Classes of Symmetry, by Mr. H. Hilton. — Specimens of 
Turnerite from Cornwall were exhibited by Mr. Russell, and crystals 
of Sartorite by Dr. Trechmann. 
CORRESPONDENCE. 
THE SOMABULA DIAMOND FIELD. 
Srr,—I notice in your December issue! a comment by Dr. Flett on 
my paper on the Somabula Diamond Field, and I take this opportunity 
of expressing my regret that it was published just before a further 
visit to the field under the more favourable conditions now prevailing. 
It is unquestionable, as Dr. Flett implies, that most of the mineral 
locally regarded as enstatite is really staurolitea It did not oceur to 
me to doubt the original determination of this mineral as a rhombic 
pyroxene, until I recently secured some fragments with faces showing 
the characteristic angles of staurolite. Andalusite may also be added 
to the list of what I have termed ‘‘ unequivocal contact. minerals.”’ 
There can be no doubt, in fact, that the characteristic minerals of the 
alluvial deposit come chiefly trom the margins of the granite mass 
which it overlies. 
But this does not in the least alter the position as regards the 
original source of the diamonds. It is significant, for instance, that 
though diamond is almost exactly of the same specific gravity as 
chrysoberyl, topaz, and staurolite, the quantity of these latter has no 
relation whatever to the abundance or even to the presence of the 
diamond. The only mineral which shows indications of such a 
relationship is garnet, a possible ‘ pipe’ mineral, by the way. The 
sapphires, rubies, and chrysoberyls are also exceedingly water-worn, 
while the diamonds are in many cases perfectly unabraded, though those 
found in the present-day stream which cuts into the old alluvial are 
usually considerably worn, showing they are susceptible to wearing action. 
Perhaps a local experience of over five years and the fact of having 
made most careful field examinations of the vicinity may be permitted 
1 See Grou. Mac., December, 1906, pp. 569-570. 
