NATURE 
THURSDAY, JULY 23, 1913. 
SOUTH AFRICAN DIAMONDS. 
The Diamond Fields of Southern Africa. By Dr. 
P. A. Wagner. Pp. xxv+347+xxxvi plates. 
(Johannesburg: The Transvaal Leader; Lon- 
don: The Technical Book-Shop, 1914.) Price 
27s. 6d. ‘net. 
HIS book is a greatly enlarged edition, in 
English, of Dr. Wagner’s “Die Diamant- 
fiihrenden Gesteine Sudafrikas,’” which was pub- 
lished five years ago. The author states in his 
preface his aim to be that the book should ‘“‘con- | 
tain all that is- worth knowing ”’ concerning the 
subject of which it treats. If he has not altogether 
realised his ambition—and it is only necessary to 
glance at the list of 255 titles of works in his 
bibliography to realise the impossibility of doing 
so in a book of fewer than 350 pages—we may 
_ taining all that it is most important for prospec- 
tors, diggers, mining engineers, and investors, to 
- whom the work is specially addressed, to know. 
Geologists also will find in it a good résumé of the 
work done in connection with the rocks containing 
the diamonds. 
The first 250 pages of the book are devoted to 
an account of the primary occurrences of the dia- 
monds in South Africa. The gems were first 
discovered at the Cape in 1868, and in 1874 the | 
late Prof. Maskelyne showed that the rock in | 
which they occur is a “peridotite” containing 
olivine, enstatite, and other minerals, for which 
the late Prof. H..Carvill Lewis, in 1887, proposed 
the name of “kimberlite.” Much interest was 
aroused in 1899 by the fact established by Prof. 
Bonney, from the study of specimens obtained 
by 
actually exist embedded in masses ot “eclogite,” 
a rock made up of garnet and augite, minerals 
which are found in the kimberlite. Since that date 
much discussion has taken place as to whether 
these masses of eclogite (which have received the 
local name of “griquaite”) are nodules derived 
from a pre-existing rock or have been formed, 
like many other inclusions in the kimberlite, by a 
segregative action. Dr. Wagner suggests that a 
combination of the two hypotheses is possible and 
will best explain all the facts. 
In the second division of the book, sixty pages 
are devoted to an account of the detrital deposits 
-containing diamonds, including both those due to 
fluviatile and those due to marine action. 
latter, occurring in German South-West Africa, 
are of especial interest to geologists. At points 
Sir William Crookes, that the diamonds | 
The | 
extending along the coast for 270 miles, but no- ! 
NO. 2334, VOL. 93] 
527 
where more than twelve miles from the sea, dia- 
monds have been found. The district is nearly 
rainless and of most inhospitable character, but 
in certain valleys and depressions masses of sand 
and gravel occur yielding the diamonds—those 
obtained from these sources during the year 1913 
being of the value of nearly 3,000,000]. Among 
the geologists who have studied the district, there 
appears to be much difference of opinion as to 
whether the rocks that have yielded the diamonds 
are in the “hinterland” or are now buried be- 
neath the sea. It is. interesting to note that 
certain guano islands off the coast have yielded 
diamonds, but, up to the present, not in sufficient 
| numbers to pay the cost of prospecting. 
The third portion of the book, which deals with 
‘“Diamond Mining Companies,” does not call for 
| remark from us, but the whole work may be 
recommended as a trustworthy and up-to-date 
| treatise on the subjects with which it deals. 
admit that he has certainly produced a work con- | 
THE POPULARISATION OF EUGENICS. 
The Progress of Eugenics. By Dr. C. W. 
Saleeby. Pp. x+259. (London: Cassell and 
Go.) Etd:. 19145)) “Pree ss: set. 
R. SALEEBY divides eugenics into natural 
or primary and nurtural or secondary. 
Natural eugenics is further sub-divided into posi- 
tive, negative, and preventive. Few eugenists 
would support him in classing as eugenics much 
that he includes under the heading “nurtural,” 
yet they would agree with him in general as to the 
desirability of making as favourable as possible 
the external conditions which influence nurture 
before and after birth, and of making education a 
real preparation for all that is important in life, 
including parenthood. 
Positive eugenics means “the encouragement of 
worthy parenthood,” negative eugenics “the 
discouragement of unworthy parenthood,” and 
preventive eugenics the combating of “racial 
poisons,” venereal diseases, alcohol, and lead. In 
treating these subjects Dr. Saleeby says, “We 
must be scientific or we are lost,” and it is cer- 
tainly true that he would have succeeded better 
if he had himself maintained a more scientific 
attitude. He falls short of it in particular in that 
he appears to judge of the validity of scientific 
work by the conclusions it arrives at. When the 
conclusions seem to him desirable, the work is 
accepted readily and uncritically, as, for example, 
that of the American Eugenics Record Office on 
the inheritance of epilepsy and feeblemindedness ; 
when the conclusions seem undesirable, the work 
receives a very different treatment. Nevertheless, 
there is much contained in the book that is sensible 
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