Arkell.1956.Jurassic..

vm PREFACE
that the palaeogeographical map of the region surrounding the British
Isles which I myself accepted twenty years ago (Jurassic System in Great
Britain, 1933, pp. 595, 597) and which still appears in the latest books, is
fundamentally wrong and needs to be scrapped. Deep borings in
northern Jutland, where land had been assumed, have proved an almost
complete suite of Jurassic rocks corresponding palaeontologically, stage
by stage, with those in England, and in particular a thick Middle Jurassic
Deltaic Series like that in Yorkshire and Scotland. The area must have
formed part of the same basin as that in which the Yorkshire rocks were
laid down and could not have been cut off from it by the hypothetical
'Cimbria'. On the west the changes required are still more drastic. Here
evidence is less uncompromising, but several facts (discussed below) indicate
that in place of the hypothetical North Atlantic Continent there rolled
the North Atlantic Ocean, much as at present; in fact, Wales was merely
an island.
This being the position in respect of the area surrounding the British
Isles, I have insufficient temerity to attempt to construct maps for less
well known regions farther afield. The few that are here offered are for
the purpose of helping the reader to understand the geology and are tobe
taken as in the highest degree approximate. Usually, instead of such
hypothetical maps, I have attempted to supply sketch-maps of the actual
Jurassic outcrops. These enable the text to be followed without any
serious departure from the aim of the descriptive chapters to be primarily
a factual record.
It has been my personal experience that anyone seeking to understand
a single geological system, or even merely to determine collections of fossils
from various parts of the world, must flounder in the literature for some
twenty years before he can hope to discover all the essential published
works, and that when he has specialized for thirty years he will still be
surprised from time to time by finding overlooked papers containing
some vital pearl of information. Users of this book will be saved some
twenty years of work. It is intended for two-way use: as a guide either
to the whole Jurassic of a particular area, or to a particular stage over
the whole world. Thus anyone confronted with a Bajocian fauna for
determination can turn up all the known outcrops of the Bajocian; or,
confronted with a collection of doubtful age, he can find the important
references to all parts of the Jurassic published for that and neighbouring
areas.
While writing the book (1950-4) I have been sent for determination
collections of ammonites from England, Scotland, France, Germany,
Switzerland, Sicily, Turkey, Morocco, Algeria, Sinai, Kenya, Tanganyika,
Madagascar, Arabia, Persia, Baluchistan, Cutch, Tibet, Japan, Australia
and New Zealand. In addition I have been loaned or given by friends
and correspondents types or other specimens or casts from Canada,
Peru, Argentina and Somaliland, and have worked through small collections
in the Sedgwick Museum from Bavaria (Solnhofen Slates) and
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