Arkell.1956.Jurassic..

i6o THE ALPS AND NORTHERN CARPATHIANS
LIAS
The Lias is relatively rich in ammonites and has been far more closely
studied than the rest of the Jurassic. Because its stratigraphy is comparatively
straightforward and complete, and for the most part the faunas
are closely comparable with those of extra-Alpine Europe, it is impossible
to devote space to a stage-by-stage examination. The Prealps have been
particularly well studied. There are exhaustive monographs for the
Prealps south and west of the Rhone (Peterhans, 1926) and north and east
of the Rhone (Hug, 1898-9; Jeannet, 1912-13), and also for the klippes of
the Lake Lucerne area (Trauth, 1908). The klippes are closely comparable
faunally with the contemporary developments in the Bavarian Alps
beyond the Rhine. Jeannet (1912-13, p. 403) stressed the resemblance of
the Hettangian of the Tours d'Ai' to that of the Southern Alps of Lombardy
(Lake Lugano), but since the Hettangian shows few peculiarities, this
cannot weigh against the remarkable coincidences between the specialised
Middle Jurassic of the Prealps and that of the Briancon district in
the French Hautes Alpes (see p. 153). The chief peculiarity in the
Lias of the Prealps is the occurrence of thick breccias in the Breccia
nappe.
There is also much information on the Helvetid Lias, especially in the
Morcles nappe (Collet, 1943, 1947) and the Glarus (Trumpy, 1949).
Along the margin of the Aiguilles Rouges and parts of the Aar massifs
the Lias is absent (Collet & Parejas, 1931, pp. 5-7), as on the Vindelician
foreland farther east.
NORTH-EASTERN ALPS, VIENNA BASIN AND NORTHERN CARPATHIANS
The south-north valley of the upper Rhine, above the entry into Lake
Constance, divides the Alps into two very different halves. For once the
geological and political frontiers coincide: to the west are the Swiss and
French Alps, to the east the Austrian and Bavarian Alps. Fossiliferous
Jurassic rocks east of the Rhine occur as discontinuous shreds and patches
scattered through the Northern Limestone Alps and Dolomites, which
stretch for more than 300 miles to the gates of Vienna and are chiefly
built of thick Triassic limestones (Vetters, n.d.). Considering their great
length and narrow average width of about 30 miles, the Northern Limestone
Alps run remarkably straight, but this simplicity masks a great complexity
of structure. The apparently continuous outcrop consists, in fact, of a
mosaic of more-or-less eroded, mutually overlapping thrust-sheets, in
which the Jurassic rocks are developed in a great variety of facies, often
brought together in startling contrast by tectonic movements. To the
north, the Limestone Alps are thrust over a continuous belt of flysch,
and that in turn is thrust over the Molasse and late Tertiary foreland.
Between the Flysch and Molasse belts is a discontinuous, narrow, thrust
strip of Helvetid Mesozoics, mainly Cretaceous. (A plan of the component
nappes and of the three major tectonic belts referred to is given at the end
http://jurassic.ru/