394 



MINERALOGY. 



1'rlncipal 

 mountain 



Different 

 kindaof 

 valleys. 



Geognosy, the middle oi* the high mountain chain, and reaches to 

 the foot of the group, is denominated the principal 

 mountain chain ; the other chains either shoot from the 

 foot of the group towards the principal mountain chain, 

 but never reach the high mountain chain ; or they pro- 

 ceed from the high mountain chain, but never reach 

 the foot of the group. The principal mountain chain 

 of one group cannot join with the principal mountain 

 chain of another, nor can the high mountain chain 

 of one group join with that of another. The summit 

 of a mountain chain is denominated its ridge, and 

 that of the highest mountain chain the highest mountain 

 ridge. 



We have nearly the same circumstances to attend 

 to in regard to valleys as to mountain chains ; only 

 there is here nothing analogous to the high or middle 

 mountain chain. There are two chief kinds of valleys, 

 namely, the principal, and lateral or subordinate. The 

 principal valleys stretch uninterrupted from the high 

 mountain chain to the foot of the mountain group, and 

 those only ar"e the principal valleys that reach this point ; 

 all the others are subordinate or lateral valleys. These 

 either extend from a mountain chain to a principal val- 

 ley, or begin from a lateral chain, or the principal 

 mountain chain, and terminate at the foot of the moun- 

 tain group. Mountain chains are divided into moun- 

 tains by small valleys or ravines. In the valleys of 

 mountain groups, we have always rivers or streams, but 

 in those of mountain chains, there are either none or 

 small rivulets. The bottom of such valleys has usually 

 a very rapid ascent ; they are not deep, and are neither 

 so wide nor so extensive as true valleys, or those form- 

 ed of ranges of mountains. 



1 6. The different parts of individual mountains must 

 also be described. Almost every mountain has a. foot, 

 acclivity, and summit. By the first, we understand the 

 lowest and flattest part of a mountain. It sometimes 

 extends to a considerable distance, and then rises under 

 an angle of 8 or 10* ; when it is less extensive, or has 

 a smaller base, it rises under a somewhat greater angle, 

 but never greatly exceeds 10". The mountains in wide 

 valleys have generally a considerable foot, but those in 

 narrow valleys are less in extent. Sometimes, as in 

 mountains having a mural ascent, there is no foot. 



The Acclivity or Ascent. By this we understand the 

 space contained between the foot and the summit of a 

 mountain. It is usually the steepest and most consi- 

 derable part of it. Its inclination is less or more than 

 30, and on this depends the greater or less covering of 

 soil. Upon an acclivity of 30 and upwards, we find a 

 good cover of soil ; at 45, however, the acclivity is too 

 great to admit the growth of trees. Sometimes the ac- 

 clivity is perpendicular, forming mural precipices ; and 

 it is either mural on one, two, or all sides, or in single 

 spots. Granite, porphyry, and sandstone, afford exam- 

 ples of such acclivities. Humboldt remarks, in regard 

 to acclivities in general, that they are to be reckoned 

 considerable when their angle is 7 or 8, which is the 

 maximum for carriages ; that they are very rapid when 

 15, which is the maximum for loaded beasts of bur- 

 then ; that an inclination of 35 is so great, that we can- 

 not ascend it without cutting steps in the rock ; and 

 that even with the aid of steps, an inclination of more 

 than 44 is very difficult of ascent. 



The Summit. This is usually the smallest part of a 

 mountain, and its inclination is generally less consider- 

 able than that of the acclivity. There occur, however, 

 exceptions to this: thus there are summits that rise 

 jnore rapidly than the acclivity ; and these are usually 



Description 

 of single 

 mountains. 



very high, almost of equal length with the acclivity, Ge.igi-.oy. 

 and completely naked. Such lofty .ind precipitous """V" 

 summits are, in Switzerland, denominated 1'caks. The 

 summit varies considerably in its sh;ipe : it is tabular, or 

 round-backed, or obtuse, or acute, or short conical. 

 Generally the shape of the mountain is characteristic 

 of the rock of which it is composed. Tims gneiss and 

 transition rocks form flat or round-backed summits ; 

 clay-slate conical summits ; and basalt and some other 

 rocks short and obtuse conical summits : granite and 

 limestone often present extremely sharp pointed sum- 

 mits or peaks. 



The summits of mountains are sometimes divided by 

 means of ravines, and these are to be considered a* 

 the smallest kind of valley. They form one extremi- 

 ty of the series of which the principal valleys in moun- 

 tain groups form the other. The inequalities formed 

 on the summits of mountains by these ravires or very 

 small valleys, are denominated Caps. A mountain may 

 have many caps, and the highest of these will be the 

 lop of the mountain. 



17. Mountain groups may be considered under five Different 

 different points of view, namely, according to their kinds of 

 length, height, breadth, shape nf the mountains, and their 'mountain 

 connection. 



18. Mountain groups, in regard to their length, may 

 be divided into principal, middle, and small. 



A principal mountain group or Alpine country must 

 be at least 130 miles long. They occur but seldom. 

 The Alps of Switzerland, the Pyrenees, and the Carpa- 

 thians, afford examples of this kind. 



A middle-sized mountain group is from 40 to 130 

 miles in length. The greater number of European 

 mountain groups belong to this class ; as examples, we 

 may mention the Grampians, Hartz, the Reisen or 

 Giant Mountains, &c. 



A small mountain group is from 10 to 40 miles in 

 length ; as examples of it, we may mention the Forest 

 of Thuringia, and the Bohemian Mittelgebirge. 



19. Mountain groups, in regard to their height, are 

 by geographers divided into high, of a middle height, 

 and low. 



A high mountain group is above 1000 toises or fa 

 thorns in height. In Europe, almost the only exam- 

 ples of this class are the Alps of Switzerland, Savoy, 

 the Tyrol, and the Pyrenees. In the Alps of Switzer- 

 land, the highest point is Mont Blanc, which is about 

 15,6'46 feet above the level of the sea. The Jungfrau- 

 horn is 1 3,730 feet above the level of the sea. In the 

 Tyrolean Alps, the Gross Glockner reaches the height 

 of 12,780 above the sea; and the Ortler 15,430. In 

 the Pyrenees, the highest point is Mont Perdu, which 

 is 1 1,283 feet above the sea. 



The elevations in South America are much more 

 considerable. Thus Antisana is 19,150; Tonguragua 

 16,579; Cotopaxi, according to Condamine, 18,890. 

 Chimborazo, the most elevated summit in the new 

 world, is 21,440 feet above the level of the sea. 



The Himalya mountain in Asia are still higher, hav- 

 ing, in some instances, an elevation of 27,000 feet. 



In Asia, Africa, and America, there appear to be 

 many mountain groups that belong to this division. 



20. Mountain groups of a middle height are from 

 500 to 1000 toises high. These are not uncommon. 

 In Germany, the Erzgebirge, Fichtelgebirge, Riesen. 

 gebirge, and Hartz, are of this magnitude. The high- 

 est point of the Fichtelgebirge is 3600 feet; of the 

 Hartz nearly the same. The Schneekoppe in the Rie 

 sengebirge is 4949 feet above the sea. 



