Koerste.J 
398 
[April 6. 
in the Vosges Mountains and the Black Forest, towards the north 
and northwest of the Bernese Jura district. The general distri- 
bution of these pebbles in the Oeningen deposits of the Alsatian 
plains and the Jura, and their occurrence even in the Swiss basin, 
is opposed to any theory advocating the existence of strong folds 
in the Jura district at this time. The pebbles in fact furnish the 
strongest evidence so far discovered for a belief in the late Ter- 
tiary origin of the Jura folds. They also suggest the existence of 
a general southern slope of the land from the Vosges Mountains 
and the Black Forest to the southern limits of the area containing 
the above mentioned igneous pebbles derived from these sources. 
They also indicate the existence in late Tertiary times of strong 
currents of water having a general southern direction, following 
the general southern slope of the land as just described. 
The entire body of evidence so far accumulated is against the 
existence of strong folds in the Jura, similar to those now charac- 
terizing its topography, until after the deposition of the Oeningen 
formations. In that case it is evident that the Jura folds are of 
comparatively recent age. 
5. Topography of the Jura Folds. — The folds of the Jura 
have a general east-northeast trend. Along the southeastern 
border, the side nearest the Alps, the folds are larger and attain 
greater altitudes. Thence north-westward they decrease in relief 
and altitude, gradually dying out as low undulations on the 
adjacent plains of France. Between the Jura and the Alps lies 
the broad valley of the Aare. No definite boundary separates the 
Jura system from the French plains. There is a tendency towards 
steeper slopes on the northern side of the folds. 
All the evidence is in favor of an origin of the folds due to 
pressure exerted from the southeast along the whole line of Jura 
folds. The more southern folds, along the Aare, are the best 
illustration of the effects of this pressure. On the northeast, 
however, the folding forces were stemmed by the Black Forest, 
so that the more northern folds, which were held back by these 
mountains on the east, were swung farther forward along their 
western continuation, and assumed a more east and west position 
than the southern folds. The result is that the western Bernese 
Jura folds have a northeast trend. The southern folds along the 
Anre valley were not held back by the Black Forest crystallines 
and therefore have the more normal east-northeast trend. The 
