386 W. G. WOOLNOUGH. 
difficult to get beginners to remember the fact, that a 
peneplain is not a mathematical plane; and the same 
difficulty seems to exist in the minds of some geologists. 
Criticisms are frequently levelled at descriptions of pene- 
plains because differences of level, amounting sometimes 
to a couple of hundred feet, are noted. 
The evolution of a perfect peneplain, while rapid in its 
earlier stages, is undoubtedly almost inconceivably slow as 
completion is approached ; and it is for this reason that, in 
most of the peneplains of Australia, various types of 
‘“‘residuals”’ of the older land surface, from which the pene- 
plain has been carved, are left standing above the general 
level. Mechanical transportation of detritus is almost 
non-existent during the later stages of erosion, by reason 
of the extremely sluggish nature of the streams. On the 
other hand, chemical weathering, and the action of solu- 
tions are strongly predominant. In another paper (in the 
press) the author has endeavoured to show that these 
phenomena, combined with the action of a copious, but 
markedly seasonal rainfall, have been necessary and 
sufficient conditions for the production of the laterite cap- 
ping which is so ubiquitous a feature throughout the length 
and breadth of Western Australia. The latter part of the 
thesis has been put forward by Simpson! and others, but, 
so farasthe author is aware, the formation of the material 
1 Simpson, E. 8., Laterite in Western Australia, Geol. Mag., Decade v, 
Vol. 1x, pp. 399 - 406, 1912. | 
Burton (Rec. Geol. Surv. India, xLv1tt, pp. 204 — 218, 1917) believes that 
the laterites of the Central Provinces of India are lacustrine in origin, 
and in this he follows Middlemiss, Wetherell, and Fermor, (references in 
paper quoted). That such cannot be the case with the laterites of 
Western Australia is clearly shown by the occurrence of fine quartz and 
aplite veins in situ in the leached “ pipe clay,” which always forms the 
foundation of the laterite of the Darling Range. It seems probable that 
two essentially different but superficially similar substances are being 
called “laterite ”’ in India and Western Australia respectively. 
