Metalliferous Beds. 33 



and the ores, or, properly speaking, the matrix of the ore 

 {ErzmitteV), appear sometimes as separate kidney and putzen 

 shaped portions in them, and are connected with the above 

 mentioned kidneys and putzen ; sometimes they form conti- 

 nuous but irregular masses, which enlarge or contract in dif- 

 ferent directions, and which are so branched that it is impos- 

 sible to assign them any definite form, and even in many cases 

 any definite direction, and all we can say is, that they lie 

 between the roof and floor, although even these can some- 

 times be recognised with difficulty. In limestone rocks they 

 sometimes appear as what the older English geologists termed 

 pipe-veins.* In very many instances, however, the mineral 

 substances of the bed are different from the mountain-mass, 

 although, nevertheless, they sometimes still stand in a certain 

 connection with it. Thus, should the bed occur in a slate rock, 

 it is found that the mineral substances of that bed are chiefly 

 quartz and calcareous spar ; more rarely, though sometimes, as 

 accompaniments to magnetic iron-ore, we have garnet, horn- 

 blende, &c. If the mountain-mass be greenstone or hornblende- 

 slate, the component parts of the bed are frequently hornblende, 

 augite, pistacite, garnet, felspar, and calcareous spar, without 

 mentioning those of more rare occurrence ; and if the rock be 

 limestone, the beds often contain calcareous spar, fluor spar, 

 heavy spar, &c. However we ought not to regard all these as uni- 

 versal, but only as generally occurring circumstances ; and we 

 ought not to neglect the careful study of the substances form- 

 ing these beds, when we are occupied with the discovery of 

 beddike repositories. The ores are generally firmly and in- 

 timately united in larger or smaller massive portions in the 

 constituent mineral substances of the beds ; frequently they 

 are found perfectly fresh, without traces of weathering, disin- 

 tegration, or any other change, and we can thus often deter- 

 mine as to a mass which has been removed from its reposi- 

 tory, if it has been derived from a bed or a vein, for in the lat- 

 ter some of these phenomena are often of a different description, 

 as the sequel will shew. But even these characters are not al- 

 ways to be trusted to, for the minerals obtained sometimes 



* Williams's Natural History of the Mineral Kingdom, vol. i. p. 331. 

 VOL. XXX. NO. LIX. JANUARY 1841. C 



