The soil formed from decomposed granites, is in ge neral comparatively unproductive.
10. Shape of Granite Mountains.—In those granite districts, in which the granite is of a loose texture, and easily acted on by the weather, the hills have a roundish form, and the lower granite tracts have a waved, or ra ther a mamillary outline.
But if very hard and indestructible granite rises through softer and more easily disintegrated, the harder portions appear in the form of peaks, needles, or in deeply dentated ridges, or cristx, and thus give rise to the bristled and denticulated aspect so peculiar to many granite districts. The valleys, in granite countries, are in general very deep, narrow, and their sides often re semble immense perpendicular walls.
Granite rocks are frequently much traversed by rents or fissures. When these rents widen by the action of the weather, the mass separates into fragments of greater or lesser magnitude, which remain long piled on each other in a most fantastic manner, often appearing like vast artificial tumuli, or masses brought together by a flood. The upper parts of the granite mountains in Arran present very striking appearances of this kind, and I have observed the same in many places of the high granite ridges of the Riesengebirge. Travellers have described similar appearances in the mountains of Swit zerland ; those of Siberia ; the Hartz; the Bohmerwald gebirge, and the Carpathians.
11. Geographical distribution of Granite.—It is one of the most frequent and widely extended rocks. It occurs in almost every mountain group, and there it frequently juts out, forming its central and highest part, having the newer primitive rocks resting on it, or placed beside it. It forms mountains in this country, as in the island of Arran, the central part of the Grampians. The ....
same is the case in the Hartz, the Riesengebirge. the Bohmerwald-gebirge, the Fichtelgebirge, and the Alps, particularly those of Savoy ; also in Bavaria, Bohemia, Franconia, Lusatia, Moravia, Upper Saxony, Thuringia, Austria, Stiria, and the Tirol. As granite is the basis on which the other primitive rocks sometimes rest, it may also appear in low mountainous situations, owing to the newer primitive rocks either not having been deposited, or having been washed away since deposition. Instances
of this we have in the Island of Arran, near Carlsbad in Bohemia, and many other places.
The following list of localities shows the known ex tent of granite in the different quarters of the globe, without, however, any reference to its forming the centre and highest, or the lowest part of mountains or mountain grou ps.
In Europe, it forms the range of Sewoga in Scandi navia; the rocks of Finland ; occurs also in Cornwall in England, in the Hartz, the Forest of Thuringia, Erzge birge in the Electorate of Saxony, the Fichtelgebirge, Lusatia, the Riesengebirge, the Bohmerwald-gebirge. the Schwarzwald (Black Forest,) the Alps of Switzer land, and Savoy ; also in the Tyrol, Salzburg, Stiria, Archduchy of Austria, the Carpathian Mountains, Auvergne, Dauphiny, Elsass, and the Pyrenean Moun tains.
In Asia, it forms the centre of Caucasus ; occurs at Kolywan, and other places in Siberia ; forms a very con siderable portion of the Uralian, Attain, and Himalya chains of mountain-groups.
In Africa, it is said to form a principal constituent part of the mountains in Upper Egypt, the Atlas Moun tains, and the country about the Cape of Good Hope.
America.—It occurs but in comparatively small quan tity in the United States ; and in Mexico, owing to the deep and high cover of porphyry, it is found only low down, as at Acapulco. In the Andes of South America, it is usually covered with gneiss, mica-slate, and traehyte, and in general is not observed higher than 6000 feet: but it abounds in the low mountains and regions of Ve nezuela, and of Parima, and descends even to the plains and to the level of the sea, as is the case on the sides of the Oroonoco, and the coasts of Peru.
In North America, it is said to occur in New York, Pennsylvania, and Virginia. In South America, it forms De los Mariches, near Caraccas, the whole Cordillera of Parima, Sierra Nevada de Merida, Torrito between South Carlos and Valencia, the country between Va lencia and Portocabello, and Cape Horn, the southern extremity of America.