444 WATEUY REE 
termed an area of ‘‘interference,” to distinguish it from the 
areas of ‘‘virgation” where fold-arcs curve away from one 
another. 
A fold-arc is not a homogeneous fold, but is made up of a 
series of unit-folds, each of which is the segmental portion of a 
curve. Any one fold, as it were, dies out in its particular 
direction and horizon, but is replaced by a fold in the next part 
of the curve passing through slightly different horizons of the 
crust. Thus the arc round which a series of unit-folds is ar- 
ranged comes under the category of curves that change their 
plane. 
In Enneberg, series of fold-arcs with their convexities towards 
different compass directions have been overcast, and the over- 
cast folds have been penetrated by reverse and normal fault- 
planes, reverse movement having taken place in the subjacent 
slices of the overcast folds. But, combined with reverse move- 
ments in virtue of vertical components, there have been converse 
movements in virtue of torsional components, so that the actual 
resultant movement has been spiral—e.g. while the middle or 
<‘arch”’ slice of an overcast fold moved in clockwise direction 
and outward, the upper and under slices of the same fold moved 
in counter-clockwise direction and inward. 
The problem resolves itself into involute and evolute move- 
ments of crust-slices with reference to central areas, the 
evolute slices tending ever to spread, the involute slices ever 
to narrow. 
Shear-breccias and fragmentary portions of folds fill up the 
inwardly-tilted troughs. The fault-rocks in certain of the sheared 
and twisted troughs of Enneberg had been formerly treated as 
independent zones of rock, and termed ‘‘ Buchenstein Agglo- 
merate”’ ; but in my paper they are shown to be practically a 
**Flysch conglomerate,” formed during the Tertiary epoch of 
Alpine upheaval. 
The “‘ Flysch”’ troughs which appear round the Alpine curves 
may possibly be explained as the result of similar processes of 
involute and evolute movements going on in slices of closely- 
piled overcast folds. Thus we might have troughs being twisted 
inwards and gathering ‘‘ Flysch”’ in variable fragments, while 
evolute slices of the reciprocal arches were being twisted out- 
wards, The ‘‘Klippen,” and even the ‘‘ Klippen” ranges, may 
represent such ‘‘arch’’ wedges of fold-arcs originally closely 
piled and jammed as the fold-arcs are round the dolomite 
massives. 
There is abundant evidence in Enneberg that the molten 
layers immediately below the crust have shared in the move- 
ments of torsional-folding. They have filled the body of the 
virgating fold-arcs produced by these movements, and have 
there been incorporated in the local crust-whirl of torsion- 
movements, finding inlet into the planes of fold-shearing, and 
being dragged and twisted along with adjacent fault-blocks. An 
inrush during earlier phases of torsion has been in its turn in- 
vaded by the next inrush, and so on, in accordance with the 
gradual progress of torsion ; the latest invasions occur along 
transverse and oblique faults, belonging to a system of faults 
which has affected Oligocene strata in the Judicarian area; 
hence such injected rock is not older than Middle Tertiary. 
The fundamental feature of torsional folding may be said to 
be centralisation ; whether it be involution of certain horizons 
in covered troughs, or evolution of other horizons in overcast 
arches, the movements have reference to the centres of torsion- 
basins and torsion: buckles. 
The principles thus demonstrated in Enneberg will be seen 
to involve the ‘‘ fan-shaped structure” of central massives. 
They could not fail to do so, since they have been deduced from 
the stratigraphy of Sella massive in Enneberg, which presents 
a wonderfully symmetrical, although obliquely elongated example 
of ‘* fan-structure.” 
I have shown in my paper on Enneberg that the transverse 
faults define a later or Tertiary series of arches and troughs, 
through whose septal portions they chiefly pass. The faults are 
shearing-planes, and are the result of oppositely-directed move- 
ments of twisting and thrusting which have taken place from 
Opposite arches upon common reciprocals, the intermediate 
troughs. These movements have produced the virgating groups 
of north and south fold-arcs which meet the east and west fold- 
arcs, and the sigmoidal combinations of torsional fold-arcs and 
fault-curves represented in Fig. 2. 
The continuance of the faulting during a protracted period of 
crust-adjustment has caused displacement of the arcs on the 
opposite sides. 
NO. 1558, VOL. 60] 
[SEPTEMBER 7, 1899 
There are several well-known lines of tranverse and oblique 
shearing through the Alps which repeat these phenomena 
on a larger scale, and at the same time no detail is wanting in 
the comparison. Some of these may be indicated :.(1) The 
Judicarian-fault ; (2) Iseo-Ortler; (3) Como-Sonthofen ; (4) 
Maggiore-Sargans ; (5) Tarentaise-Thun ; (6) Savoy-Freyburg— 
all these represent directions of inthrow and faulting along the 
*“septum”’ or ‘‘ middle limb” between great transverse arches 
and troughs which form part of major Alpine torsion-curves. 
With regard to the eastern Alps, there are also well-marked 
N.N.E.-S.S.W. directions of faulting and displacement. The 
pre-eminent example is the remarkable series of down-throws at 
the eastern limit of the Alps, with which is associated the dis- 
placement of the northern curve of the Alps towards the 
Carpathian curve. At the same time, the influence of the co- 
ordinated torsional movements round the Hungarian basin is 
evidenced in the eastern Alps by N.N.W.-S.S.E. directions 
of transverse-shearing. 
All the transverse directions of tectonic disturbance in the 
Alps have in common with the parallel Enneberg lines (a) the 
Fic. 2.—Superposition of a later series of arches and troughs upon 
an east and west series (a, s); chief result, overcasting and 
overthrusting of old and new arches over synclinal troughs. 
= ---= fold-curves and faults formed by the twisted shearing. 
virgation from them of an eastern and western series of torsion- 
curves, representing fold-arcs; (4) the injection of igneous 
rock along the main direction of ‘‘septal” shearing, associated 
with the presence of larger masses in the areas of fold-expansion ; 
(c) the fact that they have continued to act as lines of crust- 
adjustment subsequently to the period of acute torsional up- 
heaval. In the Alps the repeated displacement of the main 
chain to the north would simply indicate that the arch on the 
east of any transverse depression had been originally less 
elevated than the arch on the west of the same depression. The 
extent to which eastern curves have been twisted away from 
western curves originally belonging to the same ‘‘ bundle” of 
virgating folds, may give us some idea of the tremendous shear- 
ing that has taken place, and the great compression that the 
Alpine regions have sustained from east and west in virtue of 
this oblique, sigmoidal movement of opposite arches over 
intervening synclines (Fig. 3). 
The law which I deduced from my observations at Sella was 
that the southwardly-convex torsion curves are marked by over- 
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