Arkell.1956.Jurassic..

PREFACE
Nepal (Spiti Shales). While my judgments may be wrong, therefore,
at least they are largely first-hand.
Powerful stimuli to progress and eventual completion were provided
by collecting-tours of the Jurassic outcrops of Central Arabia in January
1951 and Algeria in January 1952. For these unforgettable experiences
I am profoundly indebted to my friends Dr R. A. Bramkamp, Chief
Geologist of the Arabian-American Oil Company, and Professor H.
Laffitte and Monsieur Gabriel Lucas, of the Laboratoire de Geologie
Appliquee, University of Algiers. In September 1953 I was also privileged
to participate as a guest in excursions of the German Geological
Society, under the leadership of Dr Helmut Holder, in the classic regions
of the Swabian Alb. To these and other friends and correspondents
who have kept me supplied with reprints and with a stream of ammonites
from all over the world, this book largely owes its existence.
A few words of explanation on arrangement and lay-out are necessary.
The guiding principle has been a purely geographical treatment by continents,
for ready reference. The only serious departure from this is the
splitting of Europe so that NE. Europe is described with northern Asia.
By this means all parts of the Boreal realm are described consecutively;
northern Asia leading on directly to Greenland and Arctic America.
If Europe were treated as an inviolate continental unit, a large part of
the Boreal realm (European Arctic and Russia) would have to be sandwiched
between parts of the Tethys. The arrangement adopted leads to
a logical sequence through Mediterranean Europe and from Spain across
the Straits of Gibraltar to North Africa, and unites the whole Tethys
except for a not-too-serious digression to East Africa. The book begins
with Britain, not from national prejudice, but because it is the type-area
for most of the stages and because it lies at the western edge of Europe
and thus provides a logical starting-point.
The boundaries between some of the continents are not so rigidly
defined by geographers as might be imagined, and I may therefore be
excused for taking some liberties: for instance, I have described Arabia
(excepting Oman) with Africa in accordance with geological practice, and
both slopes of the Caucasus with Asia. The arrangement by chapters
and sections follows natural regions with minimum reliance on political
boundaries and names, so often liable to change. Many states are not
mentioned by name, but when their geology is described they are indexed.
All tabulated and semi-tabulated stratigraphical matter is arranged
right-way-up, with youngest beds at top. The contrary practice, which
still prevails in some quarters, seems to be designed for nothing but
greater confusion.
Hundreds of ammonites of stratigraphical importance are quoted from
published figures. Many of these are redetermined from the figures,
and in such cases the revised name is given, followed by the plate and
figure reference to the work in question, without further explanation.
Thicknesses are given in metres. These have been converted where
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