2 M. Molis's Summary of Geognostical Phenomena. 



out its value in the search for useful minerals. But the rules 

 and instructions which are derived for this object from the ex- 

 ternal form of individual mountainous districts, or from indi- 

 vidual mountain ranges, or from the nature of the acclivities of 

 the valleys separating those from one another, &c., possess no 

 universality, and are merely abstracted from a few observations 

 made by those who have given such examples, and are therefore 

 chiefly local, and even in this limited point of view not to be 

 depended on. Whoever will cast a glance over the important 

 mining districts of .Joachimsthal, Freiberg, Clausthal, Schem- 

 nitz, and Redruth, will be convinced of this, and will find phe- 

 nomena, at a short distance from one another, which both sup- 

 port and contradict such rules. 



Structure of Granite. — It is of much greater importance, to 

 consider the manner in which various rocky masses or for- 

 mations are arranged in the mountainous tracts, or what is 

 generally termed the superposition {Lagerung) of these moun- 

 tain-masses. We can generally distinguish a mass which 

 forms a nucleus, or a centre in a geognostical sense, around 

 w^hich, to certain limits, the other rocky masses are arranged 

 and distributed. The centre very frequently consists of a 

 more or less extensive mass of granite, sometimes oblong, 

 and sometimes of a massive form, that is, its horizontal 

 extent is greater in one direction, or it is pretty much the 

 same in all directions. Sometimes this portion of granite is 

 the only one of this mountain-rock which makes its appearance 

 in the combination of rocks forming the tract ; but at other 

 times there are several of them, at more or less considerable 

 distances from one another, which occur on a line correspond- 

 ing more or less to the longitudinal direction of the moun- 

 tain-group ; or they lie in such a manner, that a continuous 

 straight line does not unite them. 



Generally these portions of granite occupy the high moun- 

 tain-ridges, that is, those parts of the mountain group from 

 which, towards both sides (in oblong groups), or towards all 

 sides (in massive mountain-groups), the height diminishes gra- 

 dually, though very rarely in a uniform ratio, until the base 

 of the mountains is reached. There are, however, cases in 

 which the granite masses present themselves only on one or the 



