32  Reviews—Professor A. Keith—Antiquity of Man. 
expressed in percentages of total solids, is very similar to that of 
sea-water. It is a somewhat purer solution of sodium chloride, and 
also a more concentrated solution, than sea-water, the percentage 
salinity being 5-7 (sea-water 3:5). 
The salt-flats where the springs reach the surface are devoid of 
vegetation and studded with ice-carried boulders. These are 
representative of the pre-Cambrian igneous series of North-Central 
Canada—granites, gneisses, and epidiorites. They have suffered 
intense chemical disintegration, large boulders having been reduced 
to half their original size. Different minerals have been affected to 
different extents, but not even quartz or garnet has escaped corrosion. 
Ferromagnesians have been most intensely affected; and gneissose 
structures, hardly noticeable on unweathered surfaces, stand clearly 
revealed. The striking difference between the action of these brines 
and that of sea-water calls for explanation. 
Thin crusts of salt gather, during the summer months, on the flats 
and around the boulders. The salt is somewhat deliquescent ; and 
thin films of brine are drawn, by surface tension, over the surface of 
the boulders. Water in contact with the atmosphere is a powerful 
disintegrant. Alkalies are removed as chlorides or carbonates, and 
silica and alumina are precipitated as gels, separately or in com- 
bination. The gels exercise selective adsorption on the salts of the 
brine, alkali being taken up and the brine being left richer in the 
acid radicals. The brine is thereby rendered a more active dis- 
integrating agent, and the process goes on continuously. ‘The 
function of the dissolved salts is considered to be twofold: (1) they 
provide a thin film of liquid in contact with atmospheric oxygen ; 
(2) owing to partial adsorption by colloids, they provide an acid 
residual solution, which is a powerful corrosive agent. 
The evidences of the corrosive action of sea-water on beach 
boulders are no doubt obscured by mechanical attrition due to wave 
action.. Such corrosion cannot, however, be compared in intensity 
with that of the brines. Boulders between high- and low-water 
mark are alternately submerged and dry to the base—a state of 
affairs inimical to the persistence of thin films of liquid on the surface 
of the boulders. The initial conditions are consequently wanting ; 
and the relative immunity of beach boulders from chemical corrosion 
is due, not to any inability of sea-water to act as a corrosive, but to 
the absence of favourable conditions for the activity of the solution. 
REV LHwsS- 
I.—Tue Antiquiry or Man. By Artuor Kerra, M.D., F.R.S. 
pp. 519, with 189 text-figures. London: Williams & Norgate, 
1915. Brace 10s. 6d. net. 
fP\HE subject of the antiquity of man seems naturally to fall to the 
geologist, with such aid as he can obtain from the human 
anatomist and archeologist. The value of the evidence which has to 
be considered can only be estimated by one who has a practical 
acquaintance with geological problems in the field. From Lyell 
onwards, therefore, all the most important works dealing with the 
