116 GEOGNOSY AND GEOLOGY. 
form: it may be cut up by furrows or intersected by ravines. The foot of 
the mountain, which in its slope and expansion may exhibit considerable 
diversity, experiences on the whole the same variations in the angle of 
inclination as the descent; this angle 1 is, however, different from that of the 
body. The summit or top also varies much in shape in different instances ; 
it is either acute, sharp, jagged, hunch-backed, rounded, flat, hollowed, or 
saddle-shaped. It is the manifold combinations of the different shapes of 
head, sides, and foot, that give such diversity to the appearance of 
mountains, and render it possible that,mountainous regions may appear 
different in different places; each aaa mountain may thus excite a 
fresh interest in the mind of the observer. 
2. Combinations of Mountains into Mountainous Regions and Ranges. 
It is very seldom that mountains occur entirely isolated; it is only single 
volcanic cones that are elevated abruptly from the midst of a plain. In by 
far the greater number of instances they are united into groups, and brought 
together in the most varied manner. In most cases mountains are 
arranged into what we call mountain chains. The mountain chains may 
extend in one or several directions; they may vary in length, breadth, 
height, and connexion. We can generally detect characteristics in the 
mountains which permit a distinction into two principal sections. They 
exhibit, with respect to the collocations of the mountains, either a certain 
want of system, or an arrangement according to definite laws. The first 
appearance is presented in very many hills or mountainous regions, as, for 
instance, in the extinct volcanic district of Auvergne (pl. 45, fig. 2), while 
the latter, which is of much higher interest, is a peculiarity of the mountain 
range proper. Most generally mountains occur, one after the other, so as 
to form a mountain range of greater longitudinal extent than lateral. This 
is the mountain chain as distinguished from the mountain group, which is 
of tolerably equal dimensions. The Hartz Mountains afford an illustration 
of the combination of both forms. Mountain chains are more frequently 
met with than mountain groups; this, however, does not appear to be the 
case on all the planetary bodies, as we may readily convince ourselves by 
an examination of the moon through a telescope. The immense number of 
volcanoes, with vast craters, in which again cones of eruption arise, are 
not to be mistaken in these mountain groups. In a mountain range there 
is always one part which can be distinguished as possessing the highest 
level; this is called the principal ridge, its highest portion being called the 
comb or crest. 
Mountain ranges, like single mountains, exhibit a slope equal to the mean 
value of the angle of inclination for the individual mountains. In comparing 
the parts of a system of mountains with those of a single mountain, we 
shall soon find that a parallel cannot be drawn throughout, but that in the 
former there are parts which do not similarly occur in the latter. Examples 
of these are to be seen in such systems as Monte Rosa, where the mountains 
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