Correspondence—Mr. A. J. Jukes-Browne. 385 
subsidence. For the proper estimation of the efficiency of the cause 
invoked, it is requisite that this should be clearly set forth. That 
lateral displacement by weight of accumulated sediment together 
with actual compression of the rocks below may take place in certain 
cases is extremely probable. 
The assumption of the existence of a zone of molten rock at a 
certain distance below the surface of the earth in so sensitive a con- 
dition as to respond to the weight of accumulation by becoming 
solid or that of denudation by becoming liquid is rather a large one, 
especially when the physical part is unsupported by experiment or 
quantitative determination. If these were supplied, it would be 
a fit subject for investigation, but the suggestion fails as a general 
explanation of subsidence and elevation, even if the assumptions are 
admitted, inasmuch as it does not account for the elevation of areas 
of former great sedimentation, which is one of the most striking 
facts of geology. T. Metiarp Reape. 
THE NOMENCLATURE OF AMMONITES. 
Str,—I had not much hope of converting Mr. Buckman from 
what, in common with Mr. Haddow, I conceive to be the error of 
his ways; but I wished to protest against the system of which he 
is an exponent. 
He still assumes that Afgoceras and Arietites are genera, which is 
exactly what I ventured to question. He says I do not attempt to 
discuss Lioceras, but I should have thought he would understand 
that it could be treated in the same way as Harpoceras (if it isa 
group of equal value). Let us write in catalogues Ammonites 
(Lioceras) elegans ; specialists will doubtless prefer to call it Lieceras 
elegans ; but most geologists will probably be content with Ammonites 
elegans, regarding Lioceras merely as a subgeneric name. 
My chief point, which Mr. Buckman entirely fails to notice, is 
this, that if the specialists rank Harpoceras, Lioceras. etc., as genera, 
each of them may be accredited with a species having the same 
specific name. Fancy half a dozen different Amm. elegans referable 
to an equal number of these so-called genera. 
A. J. Juxxs-Browne. 
“GEOLOGY FOR ALL.” 
Sir,— While thanking you for your notice of “ Geology for All,” 
perhaps you will permit me to say that what is called a “slip” is 
explained by the context, and is in accord with the spirit and inten- 
tion of the book, while the high per-centage of silica in orthoclase 
is duly acknowledged on page 58, where the fact is wanted. 
I may add that my aim was to find a new and intermediate path 
between the two old and well-beaten ones of Academic or Text-book 
geology and so-called ‘popular ” or entertaining geology, neither of 
which in my humble opinion is likely to lead to the end I have in 
view, namely, a general knowledge of geology by all well-educated 
people. In the days of Buckland and Hugh Miller, fossils were 
