28 M. Mohs' Summary of Geognostkal Phenomena. 



some varieties of greenstone. Both present themselves some- 

 times in such small particles, that the eye cannot at all 

 distinguish them, or at least can only do so with difficulty. 

 Hence, when we have reason to suspect the existence of 

 such metallic substances in a rock, we must subject the stony 

 mass to a more minute investigation of its composition, by 

 means of mechanical separation, and we must endeavour to be- 

 come acquainted with the extent of the repository, which, as al- 

 ready remarked, is not limited to a certain form by means of 

 fixed and recognisable limits. Sometimes the space in which 

 such minerals occur is pretty equally extended in all directions, 

 and this is the case in some of what are termed Stocktcerks ; 

 sometimes one of the dimensions is much smaller than the two 

 others, and when, therefore, we include the zone or region in 

 which the useful minerals occur between two plane surfaces 

 parallel to its greatest dimensions (which are neither present 

 as seams of stratification, nor as surfaces of distinct concre- 

 tion, or at least the circumstance is quite accidental, if the 

 latter be the case), it assumes the form of a bed, or generally 

 of a tabular repository, as is frequently observed in the gold 

 occurring in granite. 



Kidneys, Nests, Putzen, and Lying Stocks. — Another kind of 

 occurrence of the useful minerals consists therein, that they 

 present themselves either in single considerable irregular 

 masses, or that there are several at short distances from one 

 another; and, in the latter case, they may either occupy or 

 not a recognisable region. This form of occurrence belongs 

 to some iron-ores, and is observable partly in slates, and 

 partly in limestones. The smaller masses of ore are generally 

 termed kidneys or nests, and Putzen, while the larger are deno- 

 minated Lying Stocks. In the slate rocks, the structure is 

 sometimes abruptly terminated by these masses, and some- 

 times it winds arcund them, without altering generally or to 

 any extent the direction. When such small masses of ore 

 are confined to a certain region, they give the idea of a bed, 

 and then, not unfrequently, there is a clue which leads from 

 one to the other. 



Layer of Foreign Matter between the Kidneys, Sfc, and the in- 

 closing rock. — The kidneys, nests, and Putzen, sometimes exhibit 

 a phenomenon in respect to the rocks in which they occur, which 



