OF VOLCANIC ROCKS. 81 



highly disturbed and subjected to an extensive metamorphism. Tt appears that the 

 eruptive action was in a great measure, perhaps absolutely, limited to regions which 

 offered this condition. But this connection by no means justifies the conclusion that 

 the existence of metamorphic foliated rocks was among the first causes of the ejection 

 of volcanic rocks. There are not only countries, such as the mountains of Scandinavia, 

 the Ural Mountains, the Appalachians, and other ranges distinguished by the records 

 of a very ancient metamorphism, where no trace of volcanoes has been found ; but this 

 applies even to a few, though particularly grand instances of mountain ranges which 

 were the theater of metamorphic action on a grand scale within the most recent periods, 

 such as the Alps, the Himalaya, and the Pyrenees. 



The two last named relations, both conspicuous, yet both secondary in import- 

 ance, are evidently nearly identical, since granite enters, probably in all cases, into the 

 structure of those same countries which have been the theater of an extensive meta- 

 morphic action. It is, however, worthy of note that, of the regions so distinguished, 

 part of those only appear to have become the theater of eruptive activity in the Ter- 

 tiary period, where granite must, by the mode of its occurrence, be assumed to have 

 formerly been extruded to the surface, as is the case in the Sierra Nevada, on the 

 southern foot of the Alps, in middle Germany, and in central France, while no volcanic 

 rocks arrived at the surface in other mountain ranges where granite occurs only in the 

 shape of wedges surrounded by foliated rocks, and bears a merely intrusive character, 

 as in the central range of the Alps. 28 



28 Another peculiarity in the distribution of volcanic rocks may be noticed. It is their outbreak at places of dis- 

 location or faulting of mountain ranges, if we may apply these expressions for the immense displacements which some of the 

 latter have undergone, alongjines either at angles with or parallel to their direction. A remarkable instance of the first 

 kind is afforded in Hungary, where a fracture, along the line Eperies-Kaschau, crosses the Carpathians in a nearly meridional 

 direction. To the west of it, ancient formations, along with granitic, porpbyritic, and volcanic rocks, make up the surface, 

 and are elevated to high mountain ranges culminating in the High Tatra. They extend eastward close to the fracture, and 

 there terminate abruptly. East of it, the main chain of the Carpathians continues as a range of little elevation, and con- 

 sisting chiefly of Cretaceous and Eocene rocks, while the high foothills of the western part are replaced by the Hungarian 

 plains. Immediately out of the fracture rises the Eperies-Kaschau range, of nearly oue hundred miles in length, which 

 consists exclusively of volcanic rocks. The subsidence of the land on the eastern side of the fracture must have amounted 

 to several thousand feet in this case. A transverse dislocation of similar magnitude, by which the western side was sunk 

 thousands of feet, is observable on the eastern bank of the Rhine, along the boundary of Switzerland and Vorarlberg. No 

 volcanic rocks however are visible at that place, which fact appears to be in accordance with the absence of any ancient 

 eruptive rocks in the neighborhood, and the wedge-like shape of granite in the nearest places of its occurrence. A peculiar 

 instance is afforded by the three porpbyritic regions on the southern slope of the Alps, each of which indicates a deep de- 

 pression, bounded by longitudinal and transverse fractures, of that area which has in each case been the seat of eruptive 

 action. Prof. J. D. Whitney and I had occasion to observe another instance, more forcibly striking for its grandeur than 

 any of the foregoing. Following the crest of the unbroken range of the Sierra Nevada, from south-southeast to north- 

 northwest, one arrives in the northern part of the County of Plumas at a sudden change of scenery and rocks. The meta- 

 morphic rocks of the Sierra Nevada are broken off and terminate in a l;ne apparently at about right angles with the direc- 

 tion of the crest of the former. The rugged and wild scenery which they present, particularly in this county, gives way 

 abruptly to one equally remarkable for its beauty and geological interest. The high volcano, Lassen's Peak, rises in the dis- 

 tance, amidst an intensely volcanic group of hills. Low forest-clad ridges built of lava, and separated by meandering plains 

 covered by meadows, stretch southward from it, gradually sloping down towards the line of dislocation, and there abut 

 against the wall of metamorphic rocks. The whole surface, though lower than the summit range, is entirely volcanic. Sev- 

 enty miles northwest from Lassen's Peak rises Mount Shasta, more sublime even than the other. Between both is a deep 

 depression, through which the Pit River takes its course from northeast to southwest, at little altitude above the sea. 

 This depression is situated at the very place where the crest of the Sierra Nevada should pass, and is directed transversely 

 lo it. Northwest of Mount Shasta, I'mf. W. II. Brewer found the continuation of the Sierra Nevada, with similar char- 



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