Correspondence—Dr. J. W. Evans. 189 
between crossed nicols is a very low grey, and good interference- 
figures are obtained. : 
The association of minerals in the schists is the same as that 
noticed at the margin of the Ben Cruachan ‘newer granite’ mass, 
and also at the margin of ‘newer granite’ at Netherly in Elgin. 
Tourmaline, kyanite, and staurolite also occur in the Moine Schists 
of Mull, but are in no way connected with the granite. 
CORRHLSPON DEHN CEH. 
CAPE COLONY. 
Srr,—In the review of the work by Dr. Rogers and Mr. Du Toit - 
(Grot. Mac., December, 1909, p. 561) attention was called to the 
absence of references to authorities 7 the index, not in the text. 
REVIEWER. 
March 17, 1910. 
THE MEANING OF THE TERM ‘LATERITE’. 
Srr,—In discussing the meaning of the term ‘laterite’, I have at 
least the qualification of an intimate acquaintance with the material 
to which the name was first given in the area in which it is typically 
developed. 
As I understand Mr. Scrivenor, he contends that whatever may 
have been its original signification, it has been so widely employed 
in other senses that it should be dismissed from scientific language, 
the more so as the word ‘ bauxite’ is available to replace it. 
It must be remembered, however, that bauxite is a mineral name 
indicating a substance containing approximately two molecules of 
water to one of alumina, whatever may be its true chemical constitu- 
tion. ‘he bauxite of the type locality, Baux near Arles in the south 
of France, is believed to have resulted from the action of aluminium 
sulphate on limestone, but this is only one way in which such 
a product might have been formed. 
Laterite, on the other hand, is a rock name given to a widespread 
clay-like deposit which plays a conspicuous part in the surface 
features of Peninsular India. It has recently been recognized with 
similar characters in other tropical countries, and has been shown 
by the classical researches of Max Bauer, Warth, and Holland to be 
formed by the surface decomposition of alumina-bearing crystalline 
rocks, whereby the alkalies, alkaline earths, and combined silica are 
to a large extent removed, leaving behind the free silica, the titanium 
oxide, and the oxides of alumina and iron, which have taken up 
water to form hydrates. 
This well- characterized formation obviously fequires a_ special 
designation, and what could be more suitable than the name that 
Buchanan applied to it over a century ago, and which is still 
employed in the Peninsula in the same sense in scientific, technical, 
