GEOGNOSY AND GEOLOGY. 169 
Over it lie the strata of the Jura proper, whose western border passes by 
Rheims, Troyes, and Auxerre, and almost reaches Lyons. 
The Swiss Jura occupies a curve extending from Schaffhausen to below 
Geneva. It there forms high rock-walls furrowed by deep valleys of 
elevation, more abundant in the northern than in the southern portion. 
These valleys generally permit the older masses to emerge from under the 
newer. The newer strata form high lips with steep declivities, as shown in 
a valley of the French Jura (pl. 46, fig. 13). 
The structure of these valleys may be explained by a cross-section of the 
valley of Barschwyl in the Solothurn Jura (pl. 46, fig. 14). The bottom 
of the valley is formed by the gypsum bed of the keuper (6), towards which 
the keuper strata slope on both sides. Parallel to these are newer and 
newer strata, as the lias 4, the lower oolite 3, the Oxford inarl 2, the 
Portland and coral lime 1. These limestones, which are little affected by 
the decomposing influences of the atmosphere, form the precipitous lips of 
the valley. 
The Swiss Jura forms an entire system of strata curves separated by 
such valleys of elevation. The latter appear parallel for small extents, but 
in their general direction they radiate from a point not far from Basle. 
The deeper the fissure, the older is the rock which forms the bottom of the 
valley, and the more rugged the appearance of the whole. Pl. 46, fig. 15, 
is a section of a portion of the Swiss Jura. The Portland stone and coral- 
rag are indicated by 1; 2 represents the Oxford clay; 3 the lower oolite; 
4 the lias; and 5 the muschelkalk. The chain of the Weiss-stein, A, sinks 
its valleys only to the Oxford clay; the valleys of the Hauenstein, B, reach 
to the lias, as also do those of the Passwang, C. In Mont Terrible they 
extend down to the muschelkalk, which is elevated in the middle of the 
valley, D. The lips (a) formed by Portland stone and coral-rag represent the 
Hosefluh (a), and form a valley at the bottom of which lies Barschwy] (6). 
Schonthal (c) lies on the lias of the valley of the Hauenstein. The same 
lias extends under the Jura lime, cropping out first at Passwang and finally 
in the valley slope of Mont Terrible. The Renken (e) on the one side 
corresponds to the Rehhag (d) on the other. 
The German Jura is a continuation of the Swiss: it begins at Schaff- 
hausen, and extends through Franken into the vicinity of Bambere and 
Baireuth ( pl. 46, fig. 16). It describes a great arc, whose radius falls far 
in the interior of Germany. ‘The strata of the Jurassic rocks fall in the 
same direction with this radius. The German Jura is divisible into three 
classes : the black, which consists of lias, and borders the entire series; the 
brown, whose strata correspond to the Jura proper, or the inferior oolite ; 
and the white, whose masses are formed by the strata which lie over the 
coral-rag. 
In the Franconian Jura, all the coral reefs, which compose a great 
proportion of the limestone masses, are converted into dolomite, having 
there a thickness of several hundred feet. In this transformation most of 
the organic remains are so much affected as to be scarcely appreciable, 
except in certain hollow spaces filled with a loose and _finely-divided 
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