io) 
Ss RICHTHOFEN —— NATURAL SYSTEM 
continent. It appears that in Middle Germany the Triassic period designates the com- 
mencement of an era of repose, while in the Alps, where the porphyritic outbursts took 
place in the Triassic age, the Liassic strata still participated in the disturbances and 
elevations, which partly attended the porphyritic era and partly succeeded it. There- 
after followed another period distinguished by the comparatively small amount of dis- 
turbances which took place in it. Subsidence appears to have prevailed in its first part, 
while towards its end, during the second half of the Eocene epoch, that renewed rise 
commenced which contributed so much towards imparting to that mountain range its 
present configuration. In surveying the general features of the geology of Europe, it 
will be found that the changes of the boundaries of the continent and the sea, as pro- 
duced by rise and subsidence, have, in the period intermediate between the porphyritic 
and the volcanic era, been inconsiderable in proportion to the length of time; and, 
though grand in the totality of their results, they are probably far surpassed by those 
which have been produced since propylite reopened the eruptive activity. None of 
the prominent mountain ranges, it is true, have been called into existence since then, 
Some of them, of little importance and consisting completely of volcanic rocks, have 
been formed, and sedimentary formations have been folded quite extensively, so as to 
form hilly regions ; but the main ranges had existed before, and only underwent an in- 
crease in volume, though one of considerable magnitude, and the rate of elevation appears 
to have been greatest with those mountain ranges, during the period indicated, which 
have the greatest altitude at present. The amount of elevation which Eocene and 
Miocene strata have experienced in the Alps, Pyrenees, and others of the prominent 
mountain ranges justifies this conclusion, while the mode of occurrence of these forma- 
tions in the Alps allows us to infer that their central portion was elevated at a more 
rapid rate than either the northerly or the southerly part. It is worthy of note that 
not alone in the Alps, but quite generally in Europe, the Jurassic and Cretaceous 
strata have undergone only little more disturbances than those of Hocene age. In the 
belts elevated during the voleanic era, all three formations participate ordinarily at 
nearly equal rates in the structure of the low ranges of the hills stretching between 
the main ranges and girting their foot. The conclusion appears therefore to be justi- 
fied that in the volcanic belts, at least, the elevation of the Jurassic and Cretaceous 
has chiefly taken place during the volcanic era. 
There may be distinguished a twofold mode of elevation in the volcanic era: it 
manifested itself either in a secular rise of continental areas, or in the elevation of 
mountain ranges, as may be exemplified by referring to the difference in the mode of 
elevation between the Andes and the countries adjoining them to the east. 
The distinction is not so definite if we refer to the Huropean continent. Among 
the regions elevated during the voleanic era may be chiefly noticed a broad belt ex- 
tending from the Alps through the Turkish Peninsula, Asia Minor, Armenia, and 
Persia to the Himalaya, and continuing less distinct westward to the Pyrenees. The 
three main ranges have experienced the greatest amount of elevation within this belt. 
The rest of it, which is distinguished by the folding of the Nummulitic strata over its 
entire area, marks the region of the next greatest intensity of the elevating forces within 
a much more extensive area of continental rise. The increase of altitude has been com- 
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