14 M. Mohs's Summarj/ ofGeognoitical Phenomena. 



the slate series. In regard to the search for useful minerals, 

 the distinction of these mountain-masses is not a matter of such 

 indifference ; for some of the particular repositories, namely 

 some of those which are of a bed-like nature or constitution, 

 seem not only to be more frequently contained in them than in 

 the other slaty rocks, but appear to be as it were peculiar to 

 them. But it must be remarked that this circumstance is a very 

 general one, and that, therefore, it becomes necessary for us to 

 study, particularly in this respect, a district which is to be exa- 

 mined, andnot merely to transfer the result obtained in other dis- 

 tricts, even of one and the same mountain-group ; because one 

 and the same zone or region, which here consists of such moun- 

 tain-masses, or at least contains such mountain-masses in con- 

 siderable quantity, there consists of others, or contains little 

 or none of them. There is often occasion to make the obser- 

 vation, that a bed of this description (likewise of many other 

 kinds of rocks, which cannot here be specially detailed), with- 

 out possessing considerable thickness, or any other distinguish- 

 ing features, is continued for very considerable distances, dis- 

 appears here and there, or becomes so little noticeable, that 

 we can scarcely recognise it ; that afterwards, however, it 

 makes its appearance in its full extent, and that it, perhaps, 

 undergoes this change several times throughout the extent of 

 its prolongation. Although, also, there may be nothing to seek 

 for in the bed, yet not unfrequently it affords us indications 

 which will be valued by those who are engaged in pursuits of 

 this description. 



Another portion of the imbedded mountain-masses dif- 

 fers more in its nature from the slate-rocks than those of 

 which we have hitherto spoken. I allude more especially 

 to granite, porphyry, the trap rocks,* limestone, and some 



* These rocks, on account of a particular form of an-angement, in which 

 they frequently present themselves, have been regarded as of a peculiar ori- 

 gin, inasmuch as they are supposed to have issued from the interior of the 

 earth as burning liquid or molten masses. Limestone sometimes exhibits 

 the same geognostical relations. But it is not contrary to theory to attri- 

 bute the same origin to it, — an origin which, indeed, can perhaps only 

 be denied to a formation which has evidently been formed in a mecha- 

 nical way. The large granular greywacke, consisting of pebbles as large 



