142 Correspondence—Christian Tinne. 
in which channels were quickly cut was ‘‘ very much shattered by 
close jointing”. It is no doubt a little remarkable that, supposing 
these trench valleys to be, geologically speaking, rather ancient, their 
sides are not more furrowed; but water-worn valleys in the Bunter 
pebble-beds, the Neocomian Sands, and the Chalk downs of Southern 
England often have their sides unfurrowed, and cliffs of limestone, on 
a comparatively small scale in England and on a gigantic one in the 
Alps, are frequently smooth for considerable distances, showing that 
atmospheric denudation has about kept pace with that from streamlets. 
The same sometimes holds good with sandstone and granite. 
Finally, they forget that the invasion of the larger part of England 
by great ice-sheets is just as much an hypothesis as that of sub- 
mergence, and cannot be regarded as an axiom until the difficulties 
to which I have repeatedly referred have been fairly met (instead of 
being ignored) and removed. I may add that I cannot accept as 
moraines (with which I ought to be familiar) several of those to 
which some geologists give that name. But my pamphlet will fulfil 
its purpose if it leads to a more careful study of the whole question, 
instead of such reasoning as this: ‘‘ Here is a peculiar valley: how 
can we associate it with terrestrial ice-sheets?’? To me the safer 
‘method seems this: ‘‘ Here are certain physical facts: what inference 
do they suggest ?”’ Ido my best to keep ‘‘ my mind from being set 
awhirl”’ when it arrives at a conclusion which is contrary either to 
a popular opinion or to what I was taught in my younger days. 
T. G. Bonney. 
A METHOD OF HARDENING FRIABLE FOSSIL WOOD FOR 
SECTION-CUTTING. 
Sir,— While collecting from the Lower Gault in the neighbourhood 
of Farnham, Surrey, I often found fragments of what was evidently 
driftwood lying amongst the shells. It was extremely friable; in 
fact, when dry, it was, as a rule, impossible to touch it or even blow 
upon it without causing it to fall away in powder; and to obtain 
a section from such material seemed well-nigh impossible. 
When treated in the usual way with silica solution the wood did 
not appear to be permeated, but merely to be—in the mechanic’s term 
—‘case-hardened,’ that is, to have formed on the surface a very thin 
erust of hardened substance, rendering the specimen useless for 
section-cutting. 
It occurred to me, however, that a better result might be obtained 
by forcing the silica solution into the wood, on the same principle as 
that by which railway-sleepers are impregnated with creosote under 
pressure. An ordinary model steam-engine boiler was, accordingly, 
adapted for the purpose. First the filling hole was enlarged enough 
to admit a piece of the wood, and a certain fitting, stocked by all 
model makers, added. This consists of an ordinary bicycle tyre valve 
threaded on the outside to screw into the boiler. This attached, 
sufficient silica solution (undiluted) was poured in to cover the wood, 
the filler-cap screwed on, and the boiler pumped up with an ordinary 
eycle-pump. The pressure was raised to 30 lb. per square inch, 
